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Versions: (draft-richer-transactional-authz) 00 01 02

GNAP                                                      J. Richer, Ed.
Internet-Draft                                       Bespoke Engineering
Intended status: Standards Track                              A. Parecki
Expires: 21 May 2021                                                Okta
                                                              F. Imbault
                                                                acert.io
                                                        17 November 2020


              Grant Negotiation and Authorization Protocol
                    draft-ietf-gnap-core-protocol-02

Abstract

   This document defines a mechanism for delegating authorization to a
   piece of software, and conveying that delegation to the software.
   This delegation can include access to a set of APIs as well as
   information passed directly to the software.

   This document has been prepared by the GNAP working group design team
   of Kathleen Moriarty, Fabien Imbault, Dick Hardt, Mike Jones, and
   Justin Richer.  This document is intended as a starting point for the
   working group and includes decision points for discussion and
   agreement.  Many of the features in this proposed protocol can be
   accomplished in a number of ways.  Where possible, the editor has
   included notes and discussion from the design team regarding the
   options as understood.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 May 2021.







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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
     1.2.  Roles . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Elements  . . . . . . . . . . . . . . . . . . . . . . . .   6
     1.4.  Sequences . . . . . . . . . . . . . . . . . . . . . . . .   7
       1.4.1.  Redirect-based Interaction  . . . . . . . . . . . . .  10
       1.4.2.  User-code Interaction . . . . . . . . . . . . . . . .  12
       1.4.3.  Asynchronous Authorization  . . . . . . . . . . . . .  14
       1.4.4.  Software-only Authorization . . . . . . . . . . . . .  15
       1.4.5.  Refreshing an Expired Access Token  . . . . . . . . .  16
   2.  Requesting Access . . . . . . . . . . . . . . . . . . . . . .  17
     2.1.  Requesting Resources  . . . . . . . . . . . . . . . . . .  19
       2.1.1.  Requesting a Single Access Token  . . . . . . . . . .  19
       2.1.2.  Requesting Resources By Reference . . . . . . . . . .  21
       2.1.3.  Requesting Multiple Access Tokens . . . . . . . . . .  23
       2.1.4.  Signaling Token Behavior  . . . . . . . . . . . . . .  25
     2.2.  Requesting User Information . . . . . . . . . . . . . . .  26
     2.3.  Identifying the RC  . . . . . . . . . . . . . . . . . . .  27
       2.3.1.  Identifying the RC Instance . . . . . . . . . . . . .  29
       2.3.2.  Identifying the RC Key  . . . . . . . . . . . . . . .  30
       2.3.3.  Providing Displayable RC Information  . . . . . . . .  31
       2.3.4.  Authenticating the RC . . . . . . . . . . . . . . . .  31
     2.4.  Identifying the User  . . . . . . . . . . . . . . . . . .  32
       2.4.1.  Identifying the User by Reference . . . . . . . . . .  33
     2.5.  Interacting with the User . . . . . . . . . . . . . . . .  33
       2.5.1.  Redirect to an Arbitrary URL  . . . . . . . . . . . .  35
       2.5.2.  Open an Application-specific URL  . . . . . . . . . .  36
       2.5.3.  Receive a Callback After Interaction  . . . . . . . .  36
       2.5.4.  Display a Short User Code . . . . . . . . . . . . . .  38
       2.5.5.  Indicate Desired Interaction Locales  . . . . . . . .  38
       2.5.6.  Extending Interaction Modes . . . . . . . . . . . . .  39
     2.6.  Declaring RC Capabilities . . . . . . . . . . . . . . . .  39



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     2.7.  Referencing an Existing Grant Request . . . . . . . . . .  39
     2.8.  Requesting OpenID Connect Claims  . . . . . . . . . . . .  39
     2.9.  Extending The Grant Request . . . . . . . . . . . . . . .  40
   3.  Grant Response  . . . . . . . . . . . . . . . . . . . . . . .  40
     3.1.  Request Continuation  . . . . . . . . . . . . . . . . . .  42
     3.2.  Access Tokens . . . . . . . . . . . . . . . . . . . . . .  43
       3.2.1.  Single Access Token . . . . . . . . . . . . . . . . .  43
       3.2.2.  Multiple Access Tokens  . . . . . . . . . . . . . . .  46
     3.3.  Interaction Modes . . . . . . . . . . . . . . . . . . . .  47
       3.3.1.  Redirection to an arbitrary URL . . . . . . . . . . .  47
       3.3.2.  Launch of an application URL  . . . . . . . . . . . .  48
       3.3.3.  Post-interaction Callback to an RC URL  . . . . . . .  48
       3.3.4.  Display of a Short User Code  . . . . . . . . . . . .  49
       3.3.5.  Extending Interaction Mode Responses  . . . . . . . .  50
     3.4.  Returning User Information  . . . . . . . . . . . . . . .  50
     3.5.  Returning Dynamically-bound Reference Handles . . . . . .  51
     3.6.  Error Response  . . . . . . . . . . . . . . . . . . . . .  53
     3.7.  Extending the Response  . . . . . . . . . . . . . . . . .  53
   4.  Interaction at the AS . . . . . . . . . . . . . . . . . . . .  53
     4.1.  Interaction at a Redirected URI . . . . . . . . . . . . .  54
     4.2.  Interaction at the User Code URI  . . . . . . . . . . . .  54
     4.3.  Interaction through an Application URI  . . . . . . . . .  55
     4.4.  Post-Interaction Completion . . . . . . . . . . . . . . .  55
       4.4.1.  Completing Interaction with a Browser Redirect to the
               Callback URI  . . . . . . . . . . . . . . . . . . . .  56
       4.4.2.  Completing Interaction with a Direct HTTP Request
               Callback  . . . . . . . . . . . . . . . . . . . . . .  56
       4.4.3.  Calculating the interaction hash  . . . . . . . . . .  57
   5.  Continuing a Grant Request  . . . . . . . . . . . . . . . . .  58
     5.1.  Continuing After a Completed Interaction  . . . . . . . .  60
     5.2.  Continuing During Pending Interaction . . . . . . . . . .  61
     5.3.  Modifying an Existing Request . . . . . . . . . . . . . .  62
     5.4.  Getting the Current State of a Grant Request  . . . . . .  67
     5.5.  Canceling a Grant Request . . . . . . . . . . . . . . . .  68
   6.  Token Management  . . . . . . . . . . . . . . . . . . . . . .  68
     6.1.  Rotating the Access Token . . . . . . . . . . . . . . . .  69
     6.2.  Revoking the Access Token . . . . . . . . . . . . . . . .  70
   7.  Using Access Tokens . . . . . . . . . . . . . . . . . . . . .  71
   8.  Binding Keys  . . . . . . . . . . . . . . . . . . . . . . . .  72
     8.1.  Detached JWS  . . . . . . . . . . . . . . . . . . . . . .  73
     8.2.  Attached JWS  . . . . . . . . . . . . . . . . . . . . . .  75
     8.3.  Mutual TLS  . . . . . . . . . . . . . . . . . . . . . . .  79
     8.4.  Demonstration of Proof-of-Possession (DPoP) . . . . . . .  81
     8.5.  HTTP Signing  . . . . . . . . . . . . . . . . . . . . . .  82
     8.6.  OAuth Proof of Possession (PoP) . . . . . . . . . . . . .  83
   9.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . .  85
   10. Resource Servers  . . . . . . . . . . . . . . . . . . . . . .  86
     10.1.  Introspecting a Token  . . . . . . . . . . . . . . . . .  86



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     10.2.  Deriving a downstream token  . . . . . . . . . . . . . .  88
     10.3.  Registering a Resource Handle  . . . . . . . . . . . . .  89
     10.4.  Requesting Resources With Insufficient Access  . . . . .  91
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  91
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  91
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  92
   14. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  92
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  92
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  94
   Appendix B.  Component Data Models  . . . . . . . . . . . . . . .  94
   Appendix C.  Example Protocol Flows . . . . . . . . . . . . . . .  95
     C.1.  Redirect-Based User Interaction . . . . . . . . . . . . .  95
     C.2.  Secondary Device Interaction  . . . . . . . . . . . . . .  99
   Appendix D.  No User Involvement  . . . . . . . . . . . . . . . . 102
     D.1.  Asynchronous Authorization  . . . . . . . . . . . . . . . 103
     D.2.  Applying OAuth 2 Scopes and Client IDs  . . . . . . . . . 106
   Appendix E.  JSON Structures and Polymorphism . . . . . . . . . . 107
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 108

1.  Introduction

   This protocol allows a piece of software, the resource client, to
   request delegated authorization to resource servers and to request
   direct information.  This delegation is facilitated by an
   authorization server usually on behalf of a resource owner.  The
   requesting party operating the software may interact with the
   authorization server to authenticate, provide consent, and authorize
   the request.

   The process by which the delegation happens is known as a grant, and
   GNAP allows for the negotiation of the grant process over time by
   multiple parties acting in distinct roles.

   This protocol solves many of the same use cases as OAuth 2.0
   [RFC6749], OpenID Connect [OIDC], and the family of protocols that
   have grown up around that ecosystem.  However, GNAP is not an
   extension of OAuth 2.0 and is not intended to be directly compatible
   with OAuth 2.0.  GNAP seeks to provide functionality and solve use
   cases that OAuth 2.0 cannot easily or cleanly address.  Even so, GNAP
   and OAuth 2.0 will exist in parallel for many deployments, and
   considerations have been taken to facilitate the mapping and
   transition from legacy systems to GNAP.  Some examples of these can
   be found in Appendix D.2.








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1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

1.2.  Roles

   The parties in GNAP perform actions under different roles.  Roles are
   defined by the actions taken and the expectations leveraged on the
   role by the overall protocol.

   Authorization Server (AS)  Manages the requested delegations for the
      RO.  The AS issues tokens and directly delegated information to
      the RC.  The AS is defined by its grant endpoint, a single URL
      that accepts a POST request with a JSON payload.  The AS could
      also have other endpoints, including interaction endpoints and
      user code endpoints, and these are introduced to the RC as needed
      during the delegation process.

   Resource Client (RC, aka "client")  Requests tokens from the AS and
      uses tokens at the RS.  An instance of the RC software is
      identified by its key, which can be known to the AS prior to the
      first request.  The AS determines which policies apply to a given
      RC, including what it can request and on whose behalf.

   Resource Server (RS, aka "API")  Accepts tokens from the RC issued by
      the AS and serves delegated resources on behalf of the RO.  There
      could be multiple RSs protected by the AS that the RC will call.

   Resource Owner (RO)  Authorizes the request from the RC to the RS,
      often interactively at the AS.

   Requesting Party (RQ, aka "user")  Operates and interacts with the
      RC.

   The design of GNAP does not assume any one deployment architecture,
   but instead attempts to define roles that can be fulfilled in a
   number of different ways for different use cases.  As long as a given
   role fulfills all of its obligations and behaviors as defined by the
   protocol, GNAP does not make additional requirements on its structure
   or setup.

   Multiple roles can be fulfilled by the same party, and a given party
   can switch roles in different instances of the protocol.  For
   example, the RO and RQ in many instances are the same person, where a



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   user is authorizing the RC to act on their own behalf at the RS.  In
   this case, one party fulfills both of the RO and RQ roles, but the
   roles themselves are still defined separately from each other to
   allow for other use cases where they are fulfilled by different
   parties.

   For another example, in some complex scenarios, an RS receiving
   requests from one RC can act as an RC for a downstream secondary RS
   in order to fulfill the original request.  In this case, one piece of
   software is both an RS and an RC from different perspectives, and it
   fulfills these roles separately as far as the overall protocol is
   concerned.

   A single role need not be deployed as a monolithic service.  For
   example, An RC could have components that are installed on the RQ's
   device as well as a back-end system that it communicates with.  If
   both of these components participate in the delegation protocol, they
   are both considered part of the RC.

   For another example, an AS could likewise be built out of many
   constituent components in a distributed architecture.  The component
   that the RC calls directly could be different from the component that
   the the RO interacts with to drive consent, since API calls and user
   interaction have different security considerations in many
   environments.  Furthermore, the AS could need to collect identity
   claims about the RO from one system that deals with user attributes
   while generating access tokens at another system that deals with
   security rights.  From the perspective of GNAP, all of these are
   pieces of the AS and together fulfill the role of the AS as defined
   by the protocol.

   [[ See issue #29 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/29) ]]

   [[ See issue #32 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/32) ]]

1.3.  Elements

   In addition to the roles above, the protocol also involves several
   elements that are acted upon by the roles throughout the process.

   Access Token  A credential representing a set of access rights
      delegated to the RC.  The access token is created by the AS,
      consumed and verified by the RS, and issued to and carried by the
      RC.  The contents and format of the access token are opaque to the
      RC.




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   Grant  The process by which the RC requests and is given delegated
      access to the RS by the AS through the authority of the RO.

   Cryptographic Key  A cryptographic element binding a request to a
      holder of the key.  Access tokens and RC instances can be
      associated with specific keys.

   Resource  A protected API served by the RS and accessed by the RC.
      Access to this resource is delegated by the RO as part of the
      grant process.

   Subject Information  Information about the RO that is returned
      directly to the RC from the AS without the RC making a separate
      call to an RS.  Access to this information is delegated by the RO
      as part of the grant process.

   [[ See issue #33 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/33) ]]

1.4.  Sequences

   GNAP can be used in a variety of ways to allow the core delegation
   process to take place.  Many portions of this process are
   conditionally present depending on the context of the deployments,
   and not every step in this overview will happen in all circumstances.

   Note that a connection between roles in this process does not
   necessarily indicate that a specific protocol message is sent across
   the wire between the components fulfilling the roles in question, or
   that a particular step is required every time.  For example, for an
   RC interested in only getting subject information directly, and not
   calling an RS, all steps involving the RS below do not apply.

   In some circumstances, the information needed at a given stage is
   communicated out of band or is preconfigured between the components
   or entities performing the roles.  For example, one entity can fulfil
   multiple roles, and so explicit communication between the roles is
   not necessary within the protocol flow.













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        +------------+             +------------+
        | Requesting | ~ ~ ~ ~ ~ ~ |  Resource  |
        | Party (RQ) |             | Owner (RO) |
        +------------+             +------------+
            +                            +
            +                            +
           (A)                          (B)
            +                            +
            +                            +
        +--------+                       +       +------------+
        |Resource|--------------(1)------+------>|  Resource  |
        | Client |                       +       |   Server   |
        |  (RC)  |       +---------------+       |    (RS)    |
        |        |--(2)->| Authorization |       |            |
        |        |<-(3)--|     Server    |       |            |
        |        |       |      (AS)     |       |            |
        |        |--(4)->|               |       |            |
        |        |<-(5)--|               |       |            |
        |        |--------------(6)------------->|            |
        |        |       |               |<~(7)~~|            |
        |        |<-------------(8)------------->|            |
        |        |--(9)->|               |       |            |
        |        |<-(10)-|               |       |            |
        |        |--------------(11)------------>|            |
        |        |       |               |<~(12)~|            |
        |        |-(13)->|               |       |            |
        |        |       |               |       |            |
        +--------+       +---------------+       +------------+

    Legend
    + + + indicates a possible interaction with a human
    ----- indicates an interaction between protocol roles
    ~ ~ ~ indicates a potential equivalence or out-of-band communication between roles

   *  (A) The RQ interacts with the RC to indicate a need for resources
      on behalf of the RO.  This could identify the RS the RC needs to
      call, the resources needed, or the RO that is needed to approve
      the request.  Note that the RO and RQ are often the same entity in
      practice.

   *  (1) The RC attempts to call the RS (Section 10.4) to determine
      what access is needed.  The RS informs the RC that access can be
      granted through the AS.  Note that for most situations, the RC
      already knows which AS to talk to and which kinds of access it
      needs.

   *  (2) The RC requests access at the AS (Section 2).




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   *  (3) The AS processes the request and determines what is needed to
      fulfill the request.  The AS sends its response to the RC
      (Section 3).

   *  (B) If interaction is required, the AS interacts with the RO
      (Section 4) to gather authorization.  The interactive component of
      the AS can function using a variety of possible mechanisms
      including web page redirects, applications, challenge/response
      protocols, or other methods.  The RO approves the request for the
      RC being operated by the RQ.  Note that the RO and RQ are often
      the same entity in practice.

   *  (4) The RC continues the grant at the AS (Section 5).

   *  (5) If the AS determines that access can be granted, it returns a
      response to the RC (Section 3) including an access token
      (Section 3.2) for calling the RS and any directly returned
      information (Section 3.4) about the RO.

   *  (6) The RC uses the access token (Section 7) to call the RS.

   *  (7) The RS determines if the token is sufficient for the request
      by examining the token, potentially calling the AS (Section 10.1).
      Note that the RS could also examine the token directly, call an
      internal data store, execute a policy engine request, or any
      number of alternative methods for validating the token and its
      fitness for the request.

   *  (8) The RC to call the RS (Section 7) using the access token until
      the RS or RC determine that the token is no longer valid.

   *  (9) When the token no longer works, the RC fetches an updated
      access token (Section 6.1) based on the rights granted in (5).

   *  (10) The AS issues a new access token (Section 3.2) to the RC.

   *  (11) The RC uses the new access token (Section 7) to call the RS.

   *  (12) The RS determines if the new token is sufficient for the
      request by examining the token, potentially calling the AS
      (Section 10.1).

   *  (13) The RC disposes of the token (Section 6.2) once the RC has
      completed its access of the RS and no longer needs the token.

   The following sections and Appendix C contain specific guidance on
   how to use GNAP in different situations and deployments.




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1.4.1.  Redirect-based Interaction

   In this example flow, the RC is a web application that wants access
   to resources on behalf of the current user, who acts as both the
   requesting party (RQ) and the resource owner (RO).  Since the RC is
   capable of directing the user to an arbitrary URL and receiving
   responses from the user's browser, interaction here is handled
   through front-channel redirects using the user's browser.  The RC
   uses a persistent session with the user to ensure the same user that
   is starting the interaction is the user that returns from the
   interaction.

    +--------+                                  +--------+         +------+
    |   RC   |                                  |   AS   |         |  RO  |
    |        |                                  |        |         |  +   |
    |        |< (1) + Start Session + + + + + + + + + + + + + + + +|  RQ  |
    |        |                                  |        |         |(User)|
    |        |--(2)--- Request Access --------->|        |         |      |
    |        |                                  |        |         |      |
    |        |<-(3)-- Interaction Needed -------|        |         |      |
    |        |                                  |        |         |      |
    |        |+ (4) + Redirect for Interaction + + + + + + + + + > |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (5) +>|      |
    |        |                                  |        |  AuthN  |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (6) +>|      |
    |        |                                  |        |  AuthZ  |      |
    |        |                                  |        |         |      |
    |        |< (7) + Redirect for Continuation + + + + + + + + + +|      |
    |        |                                  |        |         +------+
    |        |--(8)--- Continue Request ------->|        |
    |        |                                  |        |
    |        |<-(9)----- Grant Access ----------|        |
    |        |                                  |        |
    +--------+                                  +--------+

   1.  The RC establishes a verifiable session to the user, in the role
       of the RQ.

   2.  The RC requests access to the resource (Section 2).  The RC
       indicates that it can redirect to an arbitrary URL
       (Section 2.5.1) and receive a callback from the browser
       (Section 2.5.3).  The RC stores verification information for its
       callback in the session created in (1).






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   3.  The AS determines that interaction is needed and responds
       (Section 3) with a URL to send the user to (Section 3.3.1) and
       information needed to verify the callback (Section 3.3.3) in (7).
       The AS also includes information the RC will need to continue the
       request (Section 3.1) in (8).  The AS associates this
       continuation information with an ongoing request that will be
       referenced in (4), (6), and (8).

   4.  The RC stores the verification and continuation information from
       (3) in the session from (1).  The RC then redirects the user to
       the URL (Section 4.1) given by the AS in (3).  The user's browser
       loads the interaction redirect URL.  The AS loads the pending
       request based on the incoming URL generated in (3).

   5.  The user authenticates at the AS, taking on the role of the RO.

   6.  As the RO, the user authorizes the pending request from the RC.

   7.  When the AS is done interacting with the user, the AS redirects
       the user back (Section 4.4.1) to the RC using the callback URL
       provided in (2).  The callback URL is augmented with an
       interaction reference that the AS associates with the ongoing
       request created in (2) and referenced in (4).  The callback URL
       is also augmented with a hash of the security information
       provided in (2) and (3).  The RC loads the verification
       information from (2) and (3) from the session created in (1).
       The RC calculates a hash (Section 4.4.3) based on this
       information and continues only if the hash validates.  Note that
       the RC needs to ensure that the parameters for the incoming
       request match those that it is expecting from the session created
       in (1).  The RC also needs to be prepared for the RQ never being
       returned to the RC and handle time outs appropriately.

   8.  The RC loads the continuation information from (3) and sends the
       interaction reference from (7) in a request to continue the
       request (Section 5.1).  The AS validates the interaction
       reference ensuring that the reference is associated with the
       request being continued.

   9.  If the request has been authorized, the AS grants access to the
       information in the form of access tokens (Section 3.2) and direct
       subject information (Section 3.4) to the RC.

   An example set of protocol messages for this method can be found in
   Appendix C.1.






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1.4.2.  User-code Interaction

   In this example flow, the RC is a device that is capable of
   presenting a short, human-readable code to the user and directing the
   user to enter that code at a known URL.  The RC is not capable of
   presenting an arbitrary URL to the user, nor is it capable of
   accepting incoming HTTP requests from the user's browser.  The RC
   polls the AS while it is waiting for the RO to authorize the request.
   The user's interaction is assumed to occur on a secondary device.  In
   this example it is assumed that the user is both the RQ and RO,
   though the user is not assumed to be interacting with the RC through
   the same web browser used for interaction at the AS.

    +--------+                                  +--------+         +------+
    |   RC   |                                  |   AS   |         |  RO  |
    |        |--(1)--- Request Access --------->|        |         |  +   |
    |        |                                  |        |         |  RQ  |
    |        |<-(2)-- Interaction Needed -------|        |         |(User)|
    |        |                                  |        |         |      |
    |        |+ (3) + + Display User Code + + + + + + + + + + + + >|      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (4) + |      |
    |        |                                  |        |Open URI |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (5) +>|      |
    |        |                                  |        |  AuthN  |      |
    |        |--(9)--- Continue Request (A) --->|        |         |      |
    |        |                                  |        |<+ (6) +>|      |
    |        |<-(10)- Not Yet Granted (Wait) ---|        |  Code   |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (7) +>|      |
    |        |                                  |        |  AuthZ  |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (8) +>|      |
    |        |                                  |        |Completed|      |
    |        |                                  |        |         |      |
    |        |--(11)-- Continue Request (B) --->|        |         +------+
    |        |                                  |        |
    |        |<-(12)----- Grant Access ---------|        |
    |        |                                  |        |
    +--------+                                  +--------+

   1.   The RC requests access to the resource (Section 2).  The RC
        indicates that it can display a user code (Section 2.5.4).

   2.   The AS determines that interaction is needed and responds
        (Section 3) with a user code to communicate to the user
        (Section 3.3.4).  This could optionally include a URL to direct



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        the user to, but this URL should be static and so could be
        configured in the RC's documentation.  The AS also includes
        information the RC will need to continue the request
        (Section 3.1) in (8) and (10).  The AS associates this
        continuation information with an ongoing request that will be
        referenced in (4), (6), (8), and (10).

   3.   The RC stores the continuation information from (2) for use in
        (8) and (10).  The RC then communicates the code to the user
        (Section 4.1) given by the AS in (2).

   4.   The user's directs their browser to the user code URL.  This URL
        is stable and can be communicated via the RC's documentation,
        the AS documentation, or the RC software itself.  Since it is
        assumed that the RO will interact with the AS through a
        secondary device, the RC does not provide a mechanism to launch
        the RO's browser at this URL.

   5.   The RQ authenticates at the AS, taking on the role of the RO.

   6.   The RO enters the code communicated in (3) to the AS.  The AS
        validates this code against a current request in process.

   7.   As the RO, the user authorizes the pending request from the RC.

   8.   When the AS is done interacting with the user, the AS indicates
        to the RO that the request has been completed.

   9.   Meanwhile, the RC loads the continuation information stored at
        (3) and continues the request (Section 5).  The AS determines
        which ongoing access request is referenced here and checks its
        state.

   10.  If the access request has not yet been authorized by the RO in
        (6), the AS responds to the RC to continue the request
        (Section 3.1) at a future time through additional polled
        continuation requests.  This response can include updated
        continuation information as well as information regarding how
        long the RC should wait before calling again.  The RC replaces
        its stored continuation information from the previous response
        (2).  Note that the AS may need to determine that the RO has not
        approved the request in a sufficient amount of time and return
        an appropriate error to the RC.

   11.  The RC continues to poll the AS (Section 5.2) with the new
        continuation information in (9).





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   12.  If the request has been authorized, the AS grants access to the
        information in the form of access tokens (Section 3.2) and
        direct subject information (Section 3.4) to the RC.

   An example set of protocol messages for this method can be found in
   Appendix C.2.

1.4.3.  Asynchronous Authorization

   In this example flow, the RQ and RO roles are fulfilled by different
   parties, and the RO does not interact with the RC.  The AS reaches
   out asynchronously to the RO during the request process to gather the
   RO's authorization for the RC's request.  The RC polls the AS while
   it is waiting for the RO to authorize the request.

    +--------+                                  +--------+         +------+
    |   RC   |                                  |   AS   |         |  RO  |
    |        |--(1)--- Request Access --------->|        |         |      |
    |        |                                  |        |         |      |
    |        |<-(2)-- Not Yet Granted (Wait) ---|        |         |      |
    |        |                                  |        |<+ (3) +>|      |
    |        |                                  |        |  AuthN  |      |
    |        |--(6)--- Continue Request (A) --->|        |         |      |
    |        |                                  |        |<+ (4) +>|      |
    |        |<-(7)-- Not Yet Granted (Wait) ---|        |  AuthZ  |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (5) +>|      |
    |        |                                  |        |Completed|      |
    |        |                                  |        |         |      |
    |        |--(8)--- Continue Request (B) --->|        |         +------+
    |        |                                  |        |
    |        |<-(9)------ Grant Access ---------|        |
    |        |                                  |        |
    +--------+                                  +--------+

   1.  The RC requests access to the resource (Section 2).  The RC does
       not send any interactions modes to the server, indicating that it
       does not expect to interact with the RO.  The RC can also signal
       which RO it requires authorization from, if known, by using the
       user request section (Section 2.4).

   2.  The AS determines that interaction is needed, but the RC cannot
       interact with the RO.  The AS responds (Section 3) with the
       information the RC will need to continue the request
       (Section 3.1) in (6) and (8), including a signal that the RC
       should wait before checking the status of the request again.  The
       AS associates this continuation information with an ongoing
       request that will be referenced in (3), (4), (5), (6), and (8).



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   3.  The AS determines which RO to contact based on the request in
       (1), through a combination of the user request (Section 2.4), the
       resources request (Section 2.1), and other policy information.
       The AS contacts the RO and authenticates them.

   4.  The RO authorizes the pending request from the RC.

   5.  When the AS is done interacting with the RO, the AS indicates to
       the RO that the request has been completed.

   6.  Meanwhile, the RC loads the continuation information stored at
       (3) and continues the request (Section 5).  The AS determines
       which ongoing access request is referenced here and checks its
       state.

   7.  If the access request has not yet been authorized by the RO in
       (6), the AS responds to the RC to continue the request
       (Section 3.1) at a future time through additional polling.  This
       response can include refreshed credentials as well as information
       regarding how long the RC should wait before calling again.  The
       RC replaces its stored continuation information from the previous
       response (2).  Note that the AS may need to determine that the RO
       has not approved the request in a sufficient amount of time and
       return an appropriate error to the RC.

   8.  The RC continues to poll the AS (Section 5.2) with the new
       continuation information from (7).

   9.  If the request has been authorized, the AS grants access to the
       information in the form of access tokens (Section 3.2) and direct
       subject information (Section 3.4) to the RC.

   An example set of protocol messages for this method can be found in
   Appendix D.1.

1.4.4.  Software-only Authorization

   In this example flow, the AS policy allows the RC to make a call on
   its own behalf, without the need for a RO to be involved at runtime
   to approve the decision.  Since there is no explicit RO, the RC does
   not interact with an RO.










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       +--------+                                  +--------+
       |   RC   |                                  |   AS   |
       |        |--(1)--- Request Access --------->|        |
       |        |                                  |        |
       |        |<-(2)---- Grant Access -----------|        |
       |        |                                  |        |
       +--------+                                  +--------+

   1.  The RC requests access to the resource (Section 2).  The RC does
       not send any interactions modes to the server.

   2.  The AS determines that the request is been authorized, the AS
       grants access to the information in the form of access tokens
       (Section 3.2) and direct subject information (Section 3.4) to the
       RC.

   An example set of protocol messages for this method can be found in
   Appendix D.

1.4.5.  Refreshing an Expired Access Token

   In this example flow, the RC receives an access token to access a
   resource server through some valid GNAP process.  The RC uses that
   token at the RS for some time, but eventually the access token
   expires.  The RC then gets a new access token by rotating the expired
   access token at the AS using the token's management URL.

       +--------+                                          +--------+
       |   RC   |                                          |   AS   |
       |        |--(1)--- Request Access ----------------->|        |
       |        |                                          |        |
       |        |<-(2)--- Grant Access --------------------|        |
       |        |                                          |        |
       |        |                             +--------+   |        |
       |        |--(3)--- Access Resource --->|   RS   |   |        |
       |        |                             |        |   |        |
       |        |<-(4)--- Error Response -----|        |   |        |
       |        |                             +--------+   |        |
       |        |                                          |        |
       |        |--(5)--- Rotate Token ------------------->|        |
       |        |                                          |        |
       |        |<-(6)--- Rotated Token -------------------|        |
       |        |                                          |        |
       +--------+                                          +--------+

   1.  The RC requests access to the resource (Section 2).





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   2.  The AS grants access to the resource (Section 3) with an access
       token (Section 3.2) usable at the RS.  The access token response
       includes a token management URI.

   3.  The RC presents the token (Section 7) to the RS.  The RS
       validates the token and returns an appropriate response for the
       API.

   4.  When the access token is expired, the RS responds to the RC with
       an error.

   5.  The RC calls the token management URI returned in (2) to rotate
       the access token (Section 6.1).  The RC presents the access token
       as well as the appropriate key.

   6.  The AS validates the rotation request including the signature and
       keys presented in (5) and returns a new access token
       (Section 3.2.1).  The response includes a new access token and
       can also include updated token management information, which the
       RC will store in place of the values returned in (2).

2.  Requesting Access

   To start a request, the RC sends JSON [RFC8259] document with an
   object as its root.  Each member of the request object represents a
   different aspect of the RC's request.  Each field is described in
   detail in a section below.

   resources (object / array of objects/strings)  Describes the rights
      that the RC is requesting for one or more access tokens to be used
      at RS's.  Section 2.1

   subject (object)  Describes the information about the RO that the RC
      is requesting to be returned directly in the response from the AS.
      Section 2.2

   client (object / string)  Describes the RC that is making this
      request, including the key that the RC will use to protect this
      request and any continuation requests at the AS and any user-
      facing information about the RC used in interactions at the AS.
      Section 2.3

   user (object / string)  Identifies the RQ to the AS in a manner that
      the AS can verify, either directly or by interacting with the RQ
      to determine their status as the RO.  Section 2.4

   interact (object)  Describes the modes that the RC has for allowing




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      the RO to interact with the AS and modes for the RC to receive
      updates when interaction is complete.  Section 2.5

   capabilities (array of strings)  Identifies named extension
      capabilities that the RC can use, signaling to the AS which
      extensions it can use.  Section 2.6

   existing_grant (string)  Identifies a previously-existing grant that
      the RC is extending with this request.  Section 2.7

   claims (object)  Identifies the identity claims to be returned as
      part of an OpenID Connect claims request.  Section 2.8

   Additional members of this request object can be defined by
   extensions to this protocol as described in Section 2.9

   A non-normative example of a grant request is below:

   {
       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata"
       ],
       "client": {
         "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
         },
         "key": {
           "proof": "jwsd",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",



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                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeL...."
           }
         }
       },
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "capabilities": ["ext1", "ext2"],
       "subject": {
           "sub_ids": ["iss_sub", "email"],
           "assertions": ["id_token"]
       }
   }

   The request MUST be sent as a JSON object in the body of the HTTP
   POST request with Content-Type "application/json", unless otherwise
   specified by the signature mechanism.

2.1.  Requesting Resources

   If the RC is requesting one or more access tokens for the purpose of
   accessing an API, the RC MUST include a "resources" field.  This
   field MUST be an array (for a single access token (Section 2.1.1)) or
   an object (for multiple access tokens (Section 2.1.3)), as described
   in the following sections.

2.1.1.  Requesting a Single Access Token

   When requesting an access token, the RC MUST send a "resources" field
   containing a JSON array.  The elements of the JSON array represent
   rights of access that the RC is requesting in the access token.  The
   requested access is the sum of all elements within the array.

   The RC declares what access it wants to associated with the resulting
   access token using objects that describe multiple dimensions of
   access.  Each object contains a "type" property that determines the
   type of API that the RC is calling.

   type (string)  The type of resource request as a string.  This field
      MAY define which other fields are allowed in the request object.
      This field is REQUIRED.



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   The value of this field is under the control of the AS.  This field
   MUST be compared using an exact byte match of the string value
   against known types by the AS.  The AS MUST ensure that there is no
   collision between different authorization data types that it
   supports.  The AS MUST NOT do any collation or normalization of data
   types during comparison.  It is RECOMMENDED that designers of
   general-purpose APIs use a URI for this field to avoid collisions
   between multiple API types protected by a single AS.

   While it is expected that many APIs will have its own properties, a
   set of common properties are defined here.  Specific API
   implementations SHOULD NOT re-use these fields with different
   semantics or syntax.  The available values for these properties are
   determined by the API being protected at the RS.

   [[ See issue #34 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/34) ]]

   actions (array of strings)  The types of actions the RC will take at
      the RS as an array of strings.  For example, an RC asking for a
      combination of "read" and "write" access.

   locations (array of strings)  The location of the RS as an array of
      strings.  These strings are typically URIs identifying the
      location of the RS.

   datatypes (array of strings)  The kinds of data available to the RC
      at the RS's API as an array of strings.  For example, an RC asking
      for access to raw "image" data and "metadata" at a photograph API.

   identifier (string)  A string identifier indicating a specific
      resource at the RS.  For example, a patient identifier for a
      medical API or a bank account number for a financial API.

   The following non-normative example shows the use of both common and
   API-specific fields as part of two different access "type" values.















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       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           }
       ]

   If this request is approved, the resulting access token
   (Section 3.2.1) will include the sum of both of the requested types
   of access.

2.1.2.  Requesting Resources By Reference

   Instead of sending an object describing the requested resource
   (Section 2.1.1), a RC MAY send a string known to the AS or RS
   representing the access being requested.  Each string SHOULD
   correspond to a specific expanded object representation at the AS.

   [[ See issue #35 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/35) ]]

       "resources": [
           "read", "dolphin-metadata", "some other thing"
       ]

   This value is opaque to the RC and MAY be any valid JSON string, and
   therefore could include spaces, unicode characters, and properly
   escaped string sequences.  However, in some situations the value is



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   intended to be seen and understood be the RC developer.  In such
   cases, the API designer choosing any such human-readable strings
   SHOULD take steps to ensure the string values are not easily confused
   by a developer

   This functionality is similar in practice to OAuth 2's "scope"
   parameter [RFC6749], where a single string represents the set of
   access rights requested by the RC.  As such, the reference string
   could contain any valid OAuth 2 scope value as in Appendix D.2.  Note
   that the reference string here is not bound to the same character
   restrictions as in OAuth 2's "scope" definition.

   A single "resources" array MAY include both object-type and string-
   type resource items.

       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "read",
           "dolphin-metadata",
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           },
           "some other thing"
       ]

   [[ See issue #36 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/36) ]]




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2.1.3.  Requesting Multiple Access Tokens

   When requesting multiple access tokens, the resources field is a JSON
   object.  The names of the JSON object fields are token identifiers
   chosen by the RC, and MAY be any valid string.  The values of the
   JSON object fields are JSON arrays representing a single access token
   request, as specified in requesting a single access token
   (Section 2.1.1).

   The following non-normative example shows a request for two separate
   access tokens, "token1" and "token2".








































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       "resources": {
           "token1": [
             {
                 "type": "photo-api",
                 "actions": [
                     "read",
                     "write",
                     "dolphin"
                 ],
                 "locations": [
                     "https://server.example.net/",
                     "https://resource.local/other"
                 ],
                 "datatypes": [
                     "metadata",
                     "images"
                 ]
             },
             "dolphin-metadata"
         ],
         "token2": [
               {
                   "type": "walrus-access",
                   "actions": [
                       "foo",
                       "bar"
                   ],
                   "locations": [
                       "https://resource.other/"
                   ],
                   "datatypes": [
                       "data",
                       "pictures",
                       "walrus whiskers"
                   ]
               }
           ]
       }

   Any approved access requests are returned in the multiple access
   token response (Section 3.2.2) structure using the token identifiers
   in the request.









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2.1.4.  Signaling Token Behavior

   While the AS is ultimately in control of how tokens are returned and
   bound to the RC, sometimes the RC has context about what it can
   support that can affect the AS's response.  This specification
   defines several flags that are passed as resource reference strings
   (Section 2.1.2).

   Each flag applies only to the single resource request in which it
   appears.

   Support of all flags is optional, such as any other resource
   reference value.

   multi_token  The RC wishes to support multiple simultaneous access
      tokens through the token rotation process.  When the RC rotates an
      access token (Section 6.1), the AS does not invalidate the
      previous access token.  The old access token continues to remain
      valid until such time as it expires or is revoked through other
      means.

   split_token  The RC is capable of receiving multiple access tokens
      (Section 3.2.2) in response to any single token request
      (Section 2.1.1), or receiving a different number of tokens than
      specified in the multiple token request (Section 2.1.3).  The
      labels of the returned additional tokens are chosen by the AS.
      The RC MUST be able to tell from the token response where and how
      it can use each of the access tokens.  [[ See issue #37
      (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/37) ]]

   bind_token  The RC wants the issued access token to be bound to the
      key the RC used (Section 2.3.2) to make the request.  The
      resulting access token MUST be bound using the same "proof"
      mechanism used by the client with a "key" value of "true",
      indicating the client's presented key is to be used for binding.
      [[ See issue #38 (https://github.com/ietf-wg-gnap/gnap-core-
      protocol/issues/38) ]]

   The AS MUST respond with any applied flags in the token response
   (Section 3.2) "resources" section.

   In this non-normative example, the requested access token is to be
   bound to the client's key and should be kept during rotation.








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       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "read",
           "bind_token",
           "multi_token"
       ]

   Additional flags can be registered in a registry TBD (Section 12).

   [[ See issue #39 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/39) ]]

2.2.  Requesting User Information

   If the RC is requesting information about the RO from the AS, it
   sends a "subject" field as a JSON object.  This object MAY contain
   the following fields (or additional fields defined in a registry TBD
   (Section 12)).

   sub_ids (array of strings)  An array of subject identifier subject
      types requested for the RO, as defined by
      [I-D.ietf-secevent-subject-identifiers].

   assertions (array of strings)  An array of requested assertion
      formats.  Possible values include "id_token" for an [OIDC] ID
      Token and "saml2" for a SAML 2 assertion.  Additional assertion
      values are defined by a registry TBD (Section 12).  [[ See issue
      #41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41)
      ]]







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   "subject": {
      "sub_ids": [ "iss_sub", "email" ],
      "assertions": [ "id_token", "saml2" ]
   }

   The AS can determine the RO's identity and permission for releasing
   this information through interaction with the RO (Section 4), AS
   policies, or assertions presented by the RC (Section 2.4).  If this
   is determined positively, the AS MAY return the RO's information in
   its response (Section 3.4) as requested.

   Subject identifiers requested by the RC serve only to identify the RO
   in the context of the AS and can't be used as communication channels
   by the RC, as discussed in Section 3.4.  One method of requesting
   communication channels and other identity claims are discussed in
   Section 2.8.

   The AS SHOULD NOT re-use subject identifiers for multiple different
   ROs.

   [[ See issue #42 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/42) ]]

   Note: the "sub_ids" and "assertions" request fields are independent
   of each other, and a returned assertion MAY omit a requested subject
   identifier.

   [[ See issue #43 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/43) ]]

2.3.  Identifying the RC

   When sending a non-continuation request to the AS, the RC MUST
   identify itself by including the "client" field of the request and by
   signing the request as described in Section 8.  Note that for a
   continuation request (Section 5), the RC instance is identified by
   its association with the request being continued and so this field is
   not sent under those circumstances.

   When RC information is sent by value, the "client" field of the
   request consists of a JSON object with the following fields.

   key (object / string)  The public key of the RC to be used in this
      request as described in Section 2.3.2.  This field is REQUIRED.

   class_id (string)  An identifier string that the AS can use to





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      identify the software comprising this instance of the RC.  The
      contents and format of this field are up to the AS.  This field is
      OPTIONAL.

   display (object)  An object containing additional information that
      the AS MAY display to the RO during interaction, authorization,
      and management.  This field is OPTIONAL.

"client": {
    "key": {
        "proof": "httpsig",
        "jwk": {
                    "kty": "RSA",
                    "e": "AQAB",
                    "kid": "xyz-1",
                    "alg": "RS256",
                    "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
        },
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
    },
    "class_id": "web-server-1234",
    "display": {
        "name": "My Client Display Name",
        "uri": "https://example.net/client"
    }
}

   Additional fields are defined in a registry TBD (Section 12).

   The RC MUST prove possession of any presented key by the "proof"
   mechanism associated with the key in the request.  Proof types are
   defined in a registry TBD (Section 12) and an initial set of methods
   is described in Section 8.

   Note that the AS MAY know the RC's public key ahead of time, and the
   AS MAY apply different policies to the request depending on what has
   been registered against that key.  If the same public key is sent by
   value on subsequent access requests, the AS SHOULD treat these
   requests as coming from the same RC software instance for purposes of
   identification, authentication, and policy application.  If the AS
   does not know the RC's public key ahead of time, the AS MAY accept or
   reject the request based on AS policy, attestations within the client
   request, and other mechanisms.

   [[ See issue #44 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/44) ]]





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2.3.1.  Identifying the RC Instance

   If the RC has an instance identifier that the AS can use to determine
   appropriate key information, the RC can send this value in the
   "instance_id" field.  The instance identifier MAY be assigned to an
   RC instance at runtime through the Section 3.5 or MAY be obtained in
   another fashion, such as a static registration process at the AS.

   instance_id (string)  An identifier string that the AS can use to
      identify the particular instance of this RC.  The content and
      structure of this identifier is opaque to the RC.

   "client": {
       "instance_id": "client-541-ab"
   }

   If there are no additional fields to send, the RC MAY send the
   instance identifier as a direct reference value in lieu of the
   object.

   "client": "client-541-ab"

   When the AS receives a request with an instance identifier, the AS
   MUST ensure that the key used to sign the request (Section 8) is
   associated with the instance identifier.

   If the "instance_id" field is sent, it MUST NOT be accompanied by
   other fields unless such fields are explicitly marked safe for
   inclusion alongside the instance identifier.

   [[ See issue #45 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/45) ]]

   If the AS does not recognize the instance identifier, the request
   MUST be rejected with an error.

   If the RC instance is identified in this manner, the registered key
   for the RC MAY be a symmetric key known to the AS.  The RC MUST NOT
   send a symmetric key by value in the request, as doing so would
   expose the key directly instead of proving possession of it.

   [[ See issue #46 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/46) ]]








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2.3.2.  Identifying the RC Key

   The RC key MUST be a public key in at least one supported format and
   MUST be applicable to the proofing mechanism used in the request.  If
   the key is sent in multiple formats, all the keys MUST be the same.
   The key presented in this field MUST be the key used to sign the
   request.

   proof (string)  The form of proof that the RC will use when
      presenting the key to the AS.  The valid values of this field and
      the processing requirements for each are detailed in Section 8.
      This field is REQUIRED.

   jwk (object)  Value of the public key as a JSON Web Key. MUST contain
      an "alg" field which is used to validate the signature.  MUST
      contain the "kid" field to identify the key in the signed object.

   cert (string)  PEM serialized value of the certificate used to sign
      the request, with optional internal whitespace.

   cert#S256 (string)  The certificate thumbprint calculated as per
      OAuth-MTLS [RFC8705] in base64 URL encoding.

   Additional key types are defined in a registry TBD (Section 12).

   [[ See issue #47 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/47) ]]

   This non-normative example shows a single key presented in multiple
   formats using a single proofing mechanism.

    "key": {
        "proof": "jwsd",
        "jwk": {
                    "kty": "RSA",
                    "e": "AQAB",
                    "kid": "xyz-1",
                    "alg": "RS256",
                    "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
        },
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA..."
    }

   Continuation requests (Section 5) MUST use the same key (or its most
   recent rotation) and proof method as the initial request.






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2.3.3.  Providing Displayable RC Information

   If the RC has additional information to display to the RO during any
   interactions at the AS, it MAY send that information in the "display"
   field.  This field is a JSON object that declares information to
   present to the RO during any interactive sequences.

   name (string)  Display name of the RC software

   uri (string)  User-facing web page of the RC software

   logo_uri (string)  Display image to represent the RC software

       "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       }

   [[ See issue #48 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/48) ]]

   Additional display fields are defined by a registry TBD (Section 12).

   The AS SHOULD use these values during interaction with the RO.  The
   values are for informational purposes only and MUST NOT be taken as
   authentic proof of the RC's identity or source.  The AS MAY restrict
   display values to specific RC instances, as identified by their keys
   in Section 2.3.

2.3.4.  Authenticating the RC

   If the presented key is known to the AS and is associated with a
   single instance of the RC software, the process of presenting a key
   and proving possession of that key is sufficient to authenticate the
   RC to the AS.  The AS MAY associate policies with the RC software
   identified by this key, such as limiting which resources can be
   requested and which interaction methods can be used.  For example,
   only specific RCs with certain known keys might be trusted with
   access tokens without the AS interacting directly with the RO as in
   Appendix D.

   The presentation of a key allows the AS to strongly associate
   multiple successive requests from the same RC with each other.  This
   is true when the AS knows the key ahead of time and can use the key
   to authenticate the RC software, but also if the key is ephemeral and
   created just for this series of requests.  As such the AS MAY allow
   for RCs to make requests with unknown keys.  This pattern allows for
   ephemeral RCs, such as single-page applications, and RCs with many



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   individual instances, such as mobile applications, to generate their
   own key pairs and use them within the protocol without having to go
   through a separate registration step.  The AS MAY limit which
   capabilities are made available to RCs with unknown keys.  For
   example, the AS could have a policy saying that only previously-
   registered RCs can request particular resources, or that all RCs with
   unknown keys have to be interactively approved by an RO.

2.4.  Identifying the User

   If the RC knows the identity of the RQ through one or more
   identifiers or assertions, the RC MAY send that information to the AS
   in the "user" field.  The RC MAY pass this information by value or by
   reference.

   sub_ids (array of strings)  An array of subject identifiers for the
      RQ, as defined by [I-D.ietf-secevent-subject-identifiers].

   assertions (object)  An object containing assertions as values keyed
      on the assertion type defined by a registry TBD (Section 12).
      Possible keys include "id_token" for an [OIDC] ID Token and
      "saml2" for a SAML 2 assertion.  Additional assertion values are
      defined by a registry TBD (Section 12).  [[ See issue #41
      (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/41) ]]

   "user": {
      "sub_ids": [ {
        "subject_type": "email",
        "email": "user@example.com"
      } ],
      "assertions": {
        "id_token": "eyj..."
      }
   }

   Subject identifiers are hints to the AS in determining the RO and
   MUST NOT be taken as declarative statements that a particular RO is
   present at the RC and acting as the RQ.  Assertions SHOULD be
   validated by the AS.  [[ See issue #49 (https://github.com/ietf-wg-
   gnap/gnap-core-protocol/issues/49) ]]

   If the identified RQ does not match the RO present at the AS during
   an interaction step, the AS SHOULD reject the request with an error.

   [[ See issue #50 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/50) ]]





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   If the AS trusts the RC to present verifiable assertions, the AS MAY
   decide, based on its policy, to skip interaction with the RO, even if
   the RC provides one or more interaction modes in its request.

2.4.1.  Identifying the User by Reference

   User reference identifiers can be dynamically issued by the AS
   (Section 3.5) to allow the RC to represent the same RQ to the AS over
   subsequent requests.

   If the RC has a reference for the RQ at this AS, the RC MAY pass that
   reference as a string.  The format of this string is opaque to the
   RC.

   "user": "XUT2MFM1XBIKJKSDU8QM"

   User reference identifiers are not intended to be human-readable user
   identifiers or structured assertions.  For the RC to send either of
   these, use the full user request object (Section 2.4) instead.

   [[ See issue #51 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/51) ]]

   If the AS does not recognize the user reference, it MUST return an
   error.

2.5.  Interacting with the User

   Many times, the AS will require interaction with the RO in order to
   approve a requested delegation to the RC for both resources and
   direct claim information.  Many times the RQ using the RC is the same
   person as the RO, and the RC can directly drive interaction with the
   AS by redirecting the RQ on the same device, or by launching an
   application.  Other times, the RC can provide information to start
   the RO's interaction on a secondary device, or the RC will wait for
   the RO to approve the request asynchronously.  The RC could also be
   signaled that interaction has completed by the AS making callbacks.
   To facilitate all of these modes, the RC declares the means that it
   can interact using the "interact" field.

   The "interact" field is a JSON object with keys that declare
   different interaction modes.  A RC MUST NOT declare an interaction
   mode it does not support.  The RC MAY send multiple modes in the same
   request.  There is no preference order specified in this request.  An
   AS MAY respond to any, all, or none of the presented interaction
   modes (Section 3.3) in a request, depending on its capabilities and
   what is allowed to fulfill the request.  This specification defines
   the following interaction modes:



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   redirect (boolean)  Indicates that the RC can direct the RQ to an
      arbitrary URL at the AS for interaction.  Section 2.5.1

   app (boolean)  Indicates that the RC can launch an application on the
      RQ's device for interaction.  Section 2.5.2

   callback (object)  Indicates that the RC can receive a callback from
      the AS after interaction with the RO has concluded.  Section 2.5.3

   user_code (boolean)  Indicates that the RC can communicate a human-
      readable short code to the RQ for use with a stable URL at the AS.
      Section 2.5.4

   ui_locales (array of strings)  Indicates the RQ's preferred locales
      that the AS can use during interaction, particularly before the RO
      has authenticated.  Section 2.5.5

   The following sections detail requests for interaction modes.
   Additional interaction modes are defined in a registry TBD
   (Section 12).

   [[ See issue #52 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/52) ]]

   In this non-normative example, the RC is indicating that it can
   redirect (Section 2.5.1) the RQ to an arbitrary URL and can receive a
   callback (Section 2.5.3) through a browser request.

       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }

   In this non-normative example, the RC is indicating that it can
   display a user code (Section 2.5.4) and direct the RQ to an arbitrary
   URL of maximum length (Section 2.5.1.1) 255 characters, but it cannot
   accept a callback.

       "interact": {
           "redirect": 255,
           "user_code": true
       }





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   If the RC does not provide a suitable interaction mechanism, the AS
   cannot contact the RO asynchronously, and the AS determines that
   interaction is required, then the AS SHOULD return an error since the
   RC will be unable to complete the request without authorization.

   The AS SHOULD apply suitable timeouts to any interaction mechanisms
   provided, including user codes and redirection URLs.  The RC SHOULD
   apply suitable timeouts to any callback URLs.

2.5.1.  Redirect to an Arbitrary URL

   If the RC is capable of directing the RQ to a URL defined by the AS
   at runtime, the RC indicates this by sending the "redirect" field
   with the boolean value "true".  The means by which the RC will
   activate this URL is out of scope of this specification, but common
   methods include an HTTP redirect, launching a browser on the RQ's
   device, providing a scannable image encoding, and printing out a URL
   to an interactive console.

   "interact": {
      "redirect": true
   }

   If this interaction mode is supported for this RC and request, the AS
   returns a redirect interaction response Section 3.3.1.

2.5.1.1.  Redirect to an Arbitrary Shortened URL

   If the RC would prefer to redirect to a shortened URL defined by the
   AS at runtime, the RC indicates this by sending the "redirect" field
   with an integer indicating the maximum character length of the
   returned URL.  The AS MAY use this value to decide whether to return
   a shortened form of the response URL.  If the AS cannot shorten its
   response URL enough to fit in the requested size, the AS SHOULD
   return an error.  [[ See issue #53 (https://github.com/ietf-wg-gnap/
   gnap-core-protocol/issues/53) ]]

   "interact": {
      "redirect": 255
   }

   If this interaction mode is supported for this RC and request, the AS
   returns a redirect interaction response with short URL Section 3.3.1.








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2.5.2.  Open an Application-specific URL

   If the RC can open a URL associated with an application on the RQ's
   device, the RC indicates this by sending the "app" field with boolean
   value "true".  The means by which the RC determines the application
   to open with this URL are out of scope of this specification.

   "interact": {
      "app": true
   }

   If this interaction mode is supported for this RC and request, the AS
   returns an app interaction response with an app URL payload
   Section 3.3.2.

   [[ See issue #54 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/54) ]]

2.5.3.  Receive a Callback After Interaction

   If the RC is capable of receiving a message from the AS indicating
   that the RO has completed their interaction, the RC indicates this by
   sending the "callback" field.  The value of this field is an object
   containing the following members.

   uri (string)  REQUIRED.  Indicates the URI to send the RO to after
      interaction.  This URI MAY be unique per request and MUST be
      hosted by or accessible by the RC.  This URI MUST NOT contain any
      fragment component.  This URI MUST be protected by HTTPS, be
      hosted on a server local to the RO's browser ("localhost"), or use
      an application-specific URI scheme.  If the RC needs any state
      information to tie to the front channel interaction response, it
      MUST use a unique callback URI to link to that ongoing state.  The
      allowable URIs and URI patterns MAY be restricted by the AS based
      on the RC's presented key information.  The callback URI SHOULD be
      presented to the RO during the interaction phase before redirect.
      [[ See issue #55 (https://github.com/ietf-wg-gnap/gnap-core-
      protocol/issues/55) ]]

   nonce (string)  REQUIRED.  Unique value to be used in the calculation
      of the "hash" query parameter sent to the callback URL, must be
      sufficiently random to be unguessable by an attacker.  MUST be
      generated by the RC as a unique value for this request.

   method (string)  REQUIRED.  The callback method that the AS will use
      to contact the RC.  Valid values include "redirect"
      Section 2.5.3.1 and "push" Section 2.5.3.2, with other values
      defined by a registry TBD (Section 12).



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   hash_method (string)  OPTIONAL.  The hash calculation mechanism to be
      used for the callback hash in Section 4.4.3.  Can be one of "sha3"
      or "sha2".  If absent, the default value is "sha3".  [[ See issue
      #56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/56)
      ]]

   "interact": {
       "callback": {
          "method": "redirect",
          "uri": "https://client.example.net/return/123455",
          "nonce": "LKLTI25DK82FX4T4QFZC"
       }
   }

   If this interaction mode is supported for this RC and request, the AS
   returns a nonce for use in validating the callback response
   (Section 3.3.3).  Requests to the callback URI MUST be processed as
   described in Section 4.4, and the AS MUST require presentation of an
   interaction callback reference as described in Section 5.1.

   [[ See issue #58 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/58) ]]

   [[ See issue #59 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/59) ]]

2.5.3.1.  Receive an HTTP Callback Through the Browser

   A callback "method" value of "redirect" indicates that the RC will
   expect a call from the RO's browser using the HTTP method GET as
   described in Section 4.4.1.

   "interact": {
       "callback": {
          "method": "redirect",
          "uri": "https://client.example.net/return/123455",
          "nonce": "LKLTI25DK82FX4T4QFZC"
       }
   }

   Requests to the callback URI MUST be processed by the RC as described
   in Section 4.4.1.

   Since the incoming request to the callback URL is from the RO's
   browser, this method is usually used when the RO and RQ are the same
   entity.  As such, the RC MUST ensure the RQ is present on the request
   to prevent substitution attacks.




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2.5.3.2.  Receive an HTTP Direct Callback

   A callback "method" value of "push" indicates that the RC will expect
   a call from the AS directly using the HTTP method POST as described
   in Section 4.4.2.

   "interact": {
       "callback": {
          "method": "push",
          "uri": "https://client.example.net/return/123455",
          "nonce": "LKLTI25DK82FX4T4QFZC"
       }
   }

   Requests to the callback URI MUST be processed by the RC as described
   in Section 4.4.2.

   Since the incoming request to the callback URL is from the AS and not
   from the RO's browser, the RC MUST NOT require the RQ to be present
   on the incoming HTTP request.

   [[ See issue #60 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/60) ]]

2.5.4.  Display a Short User Code

   If the RC is capable of displaying or otherwise communicating a
   short, human-entered code to the RO, the RC indicates this by sending
   the "user_code" field with the boolean value "true".  This code is to
   be entered at a static URL that does not change at runtime, as
   described in Section 3.3.4.

   "interact": {
       "user_code": true
   }

   If this interaction mode is supported for this RC and request, the AS
   returns a user code and interaction URL as specified in Section 4.2.

2.5.5.  Indicate Desired Interaction Locales

   If the RC knows the RQ's locale and language preferences, the RC can
   send this information to the AS using the "ui_locales" field with an
   array of locale strings as defined by [RFC5646].

   "interact": {
       "ui_locales": ["en-US", "fr-CA"]
   }



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   If possible, the AS SHOULD use one of the locales in the array, with
   preference to the first item in the array supported by the AS.  If
   none of the given locales are supported, the AS MAY use a default
   locale.

2.5.6.  Extending Interaction Modes

   Additional interaction modes are defined in a registry TBD
   (Section 12).

   [[ See issue #61 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/61) ]]

2.6.  Declaring RC Capabilities

   If the RC supports extension capabilities, it MAY present them to the
   AS in the "capabilities" field.  This field is an array of strings
   representing specific extensions and capabilities, as defined by a
   registry TBD (Section 12).

   "capabilities": ["ext1", "ext2"]

2.7.  Referencing an Existing Grant Request

   If the RC has a reference handle from a previously granted request,
   it MAY send that reference in the "existing_grant" field.  This field
   is a single string consisting of the "value" of the "access_token"
   returned in a previous request's continuation response (Section 3.1).

   "existing_grant": "80UPRY5NM33OMUKMKSKU"

   The AS MUST dereference the grant associated with the reference and
   process this request in the context of the referenced one.  The AS
   MUST NOT alter the existing grant associated with the reference.

   [[ See issue #62 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/62) ]]

2.8.  Requesting OpenID Connect Claims

   If the RC and AS both support OpenID Connect's claims query language
   as defined in [OIDC] Section 5.5, the RC sends the value of the
   OpenID Connect "claims" authorization request parameter as a JSON
   object under the name "claims" in the root of the request.







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           "claims": {
                   "id_token" : {
                       "email"          : { "essential" : true },
                       "email_verified" : { "essential" : true }
                   },
                   "userinfo" : {
                       "name"           : { "essential" : true },
                       "picture"        : null
                   }
           }

   The contents of the "claims" parameter have the same semantics as
   they do in OpenID Connect's "claims" authorization request parameter,
   including all extensions such as [OIDC4IA].  The AS MUST process the
   claims object in the same way that it would with an OAuth 2 based
   authorization request.

   Note that because this is an independent query object, the "claims"
   value can augment or alter other portions of the request, namely the
   "resources" and "subject" fields.  This query language uses the
   fields in the top level of the object to indicate the target for any
   requested claims.  For instance, the "userinfo" target indicates that
   a returned access token would grant access to the given claims at the
   UserInfo Endpoint, while the "id_token" target indicates that the
   claims would be returned in an ID Token as described in Section 3.4.

   [[ See issue #63 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/63) ]]

   [[ See issue #64 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/64) ]]

2.9.  Extending The Grant Request

   The request object MAY be extended by registering new items in a
   registry TBD (Section 12).  Extensions SHOULD be orthogonal to other
   parameters.  Extensions MUST document any aspects where the extension
   item affects or influences the values or behavior of other request
   and response objects.

   [[ See issue #65 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/65) ]]

3.  Grant Response

   In response to a RC's request, the AS responds with a JSON object as
   the HTTP entity body.  Each possible field is detailed in the
   sections below



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   continue (object)  Indicates that the RC can continue the request by
      making an additional request using these parameters.  Section 3.1

   access_token (object)  A single access token that the RC can use to
      call the RS on behalf of the RO.  Section 3.2.1

   multiple_access_token (object)  Multiple named access tokens that the
      RC can use to call the RS on behalf of the RO.  Section 3.2.2

   interact (object)  Indicates that interaction through some set of
      defined mechanisms needs to take place.  Section 3.3

   subject (object)  Claims about the RO as known and declared by the
      AS.  Section 3.4

   instance_id (string)  An identifier this RC instance can use to
      identify itself when making future requests.  Section 3.5

   user_handle (string)  An identifier this RC instance can use to
      identify its current RQ when making future requests.  Section 3.5

   error (object)  An error code indicating that something has gone
      wrong.  Section 3.6

   In this example, the AS is returning an interaction URL
   (Section 3.3.1), a callback nonce (Section 3.3.3), and a continuation
   handle (Section 3.1).

{
    "interact": {
        "redirect": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
        "callback": "MBDOFXG4Y5CVJCX821LH"
    },
    "continue": {
        "access_token": {
            "value": "80UPRY5NM33OMUKMKSKU",
            "key": true
        },
        "uri": "https://server.example.com/tx"
    }
}

   In this example, the AS is returning a bearer access token
   (Section 3.2.1) with a management URL and a subject identifier
   (Section 3.4) in the form of an email address.






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{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "subject": {
        "sub_ids": [ {
           "subject_type": "email",
           "email": "user@example.com",
        } ]
    }
}

3.1.  Request Continuation

   If the AS determines that the request can be continued with
   additional requests, it responds with the "continue" field.  This
   field contains a JSON object with the following properties.

   uri (string)  REQUIRED.  The URI at which the RC can make
      continuation requests.  This URI MAY vary per request, or MAY be
      stable at the AS if the AS includes an access token.  The RC MUST
      use this value exactly as given when making a continuation request
      (Section 5).

   wait (integer)  RECOMMENDED.  The amount of time in integer seconds
      the RC SHOULD wait after receiving this continuation handle and
      calling the URI.

   access_token (object)  RECOMMENDED.  A unique access token for
      continuing the request, in the format specified in Section 3.2.1.
      This access token MUST be bound to the RC's key used in the
      request and MUST NOT be a "bearer" token.  This access token MUST
      NOT be usable at resources outside of the AS.  If the AS includes
      an access token, the RC MUST present the access token in all
      requests to the continuation URI as described in Section 7.  [[
      See issue #66 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
      issues/66) ]]












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   {
       "continue": {
           "access_token": {
               "value": "80UPRY5NM33OMUKMKSKU",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   The RC can use the values of this field to continue the request as
   described in Section 5.  Note that the RC MUST sign all continuation
   requests with its key as described in Section 8.  If the AS includes
   an "access_token", the RC MUST present the access token in its
   continuation request.

   This field SHOULD be returned when interaction is expected, to allow
   the RC to follow up after interaction has been concluded.

   [[ See issue #67 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/67) ]]

3.2.  Access Tokens

   If the AS has successfully granted one or more access tokens to the
   RC, the AS responds with either the "access_token" or the
   "multiple_access_token" field.  The AS MUST NOT respond with both the
   "access_token" and "multiple_access_token" fields.

   [[ See issue #68 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/68) ]]

3.2.1.  Single Access Token

   If the RC has requested a single access token and the AS has granted
   that access token, the AS responds with the "access_token" field.
   The value of this field is an object with the following properties.

   value (string)  REQUIRED.  The value of the access token as a string.
      The value is opaque to the RC.  The value SHOULD be limited to
      ASCII characters to facilitate transmission over HTTP headers
      within other protocols without requiring additional encoding.

   manage (string)  OPTIONAL.  The management URI for this access token.






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      If provided, the RC MAY manage its access token as described in
      Section 6.  This management URI is a function of the AS and is
      separate from the RS the RC is requesting access to.  This URI
      MUST NOT include the access token value and SHOULD be different
      for each access token issued in a request.

   resources (array of objects/strings)  RECOMMENDED.  A description of
      the rights associated with this access token, as defined in
      Section 2.1.1.  If included, this MUST reflect the rights
      associated with the issued access token.  These rights MAY vary
      from what was requested by the RC.

   expires_in (integer)  OPTIONAL.  The number of seconds in which the
      access will expire.  The RC MUST NOT use the access token past
      this time.  An RS MUST NOT accept an access token past this time.
      Note that the access token MAY be revoked by the AS or RS at any
      point prior to its expiration.

   key (object / string / boolean)  REQUIRED.  The key that the token is
      bound to.  If the boolean value "true" is used, the token is bound
      to the key used by the RC (Section 2.3.2) in its request for
      access.  If the boolean value "false" is used, the token is a
      bearer token with no key bound to it.  Otherwise, the key MUST be
      an object or string in a format described in Section 2.3.2,
      describing a public key to which the RC can use the associated
      private key.  The RC MUST be able to dereference or process the
      key information in order to be able to sign the request.

   The following non-normative example shows a single bearer token with
   a management URL that has access to three described resources.





















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    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            {
                "type": "photo-api",
                "actions": [
                    "read",
                    "write",
                    "dolphin"
                ],
                "locations": [
                    "https://server.example.net/",
                    "https://resource.local/other"
                ],
                "datatypes": [
                    "metadata",
                    "images"
                ]
            },
            "read", "dolphin-metadata"
        ]
    }

   The following non-normative example shows a single access token bound
   to the RC's key, which was presented using the detached JWS
   (Section 8.1) binding method.

       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "key": true,
           "resources": [
               "finance", "medical"
           ]
       }

   If the RC requested multiple access tokens (Section 2.1.3), the AS
   MUST NOT respond with a single access token structure unless the RC
   sends the "split_token" flag as described in Section 2.1.4.

   [[ See issue #69 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/69) ]]








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3.2.2.  Multiple Access Tokens

   If the RC has requested multiple access tokens and the AS has granted
   at least one of them, the AS responds with the
   "multiple_access_tokens" field.  The value of this field is a JSON
   object, and the property names correspond to the token identifiers
   chosen by the RC in the multiple access token request
   (Section 2.1.3).  The values of the properties of this object are
   access tokens as described in Section 3.2.1.

   In this non-normative example, two bearer tokens are issued under the
   names "token1" and "token2", and only the first token has a
   management URL associated with it.

    "multiple_access_tokens": {
        "token1": {
            "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
            "key": false,
            "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
        },
        "token2": {
            "value": "UFGLO2FDAFG7VGZZPJ3IZEMN21EVU71FHCARP4J1",
            "key": false
        }
    }

   Each access token corresponds to the named resources arrays in the
   RC's request (Section 2.1.3).

   The multiple access token response MUST be used when multiple access
   tokens are requested, even if only one access token is issued as a
   result of the request.  The AS MAY refuse to issue one or more of the
   requested access tokens, for any reason.  In such cases the refused
   token is omitted from the response and all of the other issued access
   tokens are included in the response the requested names appropriate
   names.

   If the RC requested a single access token (Section 2.1.1), the AS
   MUST NOT respond with the multiple access token structure unless the
   RC sends the "split_token" flag as described in Section 2.1.4.

   Each access token MAY have different proofing mechanisms.  If
   management is allowed, each access token SHOULD have different
   management URIs.

   [[ See issue #70 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/70) ]]




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3.3.  Interaction Modes

   If the RC has indicated a capability to interact with the RO in its
   request (Section 2.5), and the AS has determined that interaction is
   both supported and necessary, the AS responds to the RC with any of
   the following values in the "interact" field of the response.  There
   is no preference order for interaction modes in the response, and it
   is up to the RC to determine which ones to use.  All supported
   interaction methods are included in the same "interact" object.

   redirect (string)  Redirect to an arbitrary URL.  Section 3.3.1

   app (string)  Launch of an application URL.  Section 3.3.2

   callback (string)  Callback to an RC URL after interaction is
      completed.  Section 3.3.3

   user_code (object)  Display a short user code.  Section 3.3.4

   Additional interaction mode responses can be defined in a registry
   TBD (Section 12).

   The AS MUST NOT respond with any interaction mode that the RC did not
   indicate in its request.  The AS MUST NOT respond with any
   interaction mode that the AS does not support.  Since interaction
   responses include secret or unique information, the AS SHOULD respond
   to each interaction mode only once in an ongoing request,
   particularly if the RC modifies its request (Section 5.3).

3.3.1.  Redirection to an arbitrary URL

   If the RC indicates that it can redirect to an arbitrary URL
   (Section 2.5.1) and the AS supports this mode for the RC's request,
   the AS responds with the "redirect" field, which is a string
   containing the URL to direct the RQ to.  This URL MUST be unique for
   the request and MUST NOT contain any security-sensitive information.

     "interact": {
         "redirect": "https://interact.example.com/4CF492MLVMSW9MKMXKHQ"
     }

   The interaction URL returned represents a function of the AS but MAY
   be completely distinct from the URL the RC uses to request access
   (Section 2), allowing an AS to separate its user-interactive
   functionality from its back-end security functionality.

   [[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/72) ]]



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   The RC sends the RQ to the URL to interact with the AS.  The RC MUST
   NOT alter the URL in any way.  The means for the RC to send the RQ to
   this URL is out of scope of this specification, but common methods
   include an HTTP redirect, launching the system browser, displaying a
   scannable code, or printing out the URL in an interactive console.

3.3.2.  Launch of an application URL

   If the RC indicates that it can launch an application URL
   (Section 2.5.2) and the AS supports this mode for the RC's request,
   the AS responds with the "app" field, which is a string containing
   the URL to direct the RQ to.  This URL MUST be unique for the request
   and MUST NOT contain any security-sensitive information.

       "interact": {
           "app": "https://app.example.com/launch?tx=4CF492MLV"
       }

   The RC launches the URL as appropriate on its platform, and the means
   for the RC to launch this URL is out of scope of this specification.
   The RC MUST NOT alter the URL in any way.  The RC MAY attempt to
   detect if an installed application will service the URL being sent
   before attempting to launch the application URL.

   [[ See issue #71 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/71) ]]

3.3.3.  Post-interaction Callback to an RC URL

   If the RC indicates that it can receive a post-interaction callback
   on a URL (Section 2.5.3) and the AS supports this mode for the RC's
   request, the AS responds with a "callback" field containing a nonce
   that the RC will use in validating the callback as defined in
   Section 4.4.1.

       "interact": {
           "callback": "MBDOFXG4Y5CVJCX821LH"
       }

   [[ See issue #73 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/73) ]]

   When the RO completes interaction at the AS, the AS MUST call the
   RC's callback URL using the method indicated in the callback request
   (Section 2.5.3) as described in Section 4.4.1.






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   If the AS returns a "callback" nonce, the RC MUST NOT continue a
   grant request before it receives the associated interaction reference
   on the callback URI.

3.3.4.  Display of a Short User Code

   If the RC indicates that it can display a short user-typeable code
   (Section 2.5.4) and the AS supports this mode for the RC's request,
   the AS responds with a "user_code" field.  This field is an object
   that contains the following members.

   code (string)  REQUIRED.  A unique short code that the user can type
      into an authorization server.  This string MUST be case-
      insensitive, MUST consist of only easily typeable characters (such
      as letters or numbers).  The time in which this code will be
      accepted SHOULD be short lived, such as several minutes.  It is
      RECOMMENDED that this code be no more than eight characters in
      length.

   url (string)  RECOMMENDED.  The interaction URL that the RC will
      direct the RO to.  This URL MUST be stable at the AS such that RCs
      can be statically configured with it.

       "interact": {
           "user_code": {
               "code": "A1BC-3DFF",
               "url": "https://srv.ex/device"
           }
       }

   The RC MUST communicate the "code" to the RQ in some fashion, such as
   displaying it on a screen or reading it out audibly.  The "code" is a
   one-time-use credential that the AS uses to identify the pending
   request from the RC.  When the RO enters this code (Section 4.2) into
   the AS, the AS MUST determine the pending request that it was
   associated with.  If the AS does not recognize the entered code, the
   AS MUST display an error to the user.  If the AS detects too many
   unrecognized codes entered, it SHOULD display an error to the user.

   The RC SHOULD also communicate the URL if possible to facilitate user
   interaction, but since the URL should be stable, the RC should be
   able to safely decide to not display this value.  As this interaction
   mode is designed to facilitate interaction via a secondary device, it
   is not expected that the RC redirect the RQ to the URL given here at
   runtime.  Consequently, the URL needs to be stable enough that a RC
   could be statically configured with it, perhaps referring the RQ to
   the URL via documentation instead of through an interactive means.
   If the RC is capable of communicating an arbitrary URL to the RQ,



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   such as through a scannable code, the RC can use the "redirect"
   (Section 2.5.1) mode for this purpose instead of or in addition to
   the user code mode.

   The interaction URL returned represents a function of the AS but MAY
   be completely distinct from the URL the RC uses to request access
   (Section 2), allowing an AS to separate its user-interactive
   functionality from its back-end security functionality.

   [[ See issue #72 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/72) ]]

3.3.5.  Extending Interaction Mode Responses

   Extensions to this specification can define new interaction mode
   responses in a registry TBD (Section 12).  Extensions MUST document
   the corresponding interaction request.

3.4.  Returning User Information

   If information about the RO is requested and the AS grants the RC
   access to that data, the AS returns the approved information in the
   "subject" response field.  This field is an object with the following
   OPTIONAL properties.

   sub_ids (array of strings)  An array of subject identifiers for the
      RO, as defined by [I-D.ietf-secevent-subject-identifiers].  [[ See
      issue #74 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
      issues/74) ]]

   assertions (object)  An object containing assertions as values keyed
      on the assertion type defined by a registry TBD (Section 12).  [[
      See issue #41 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
      issues/41) ]]

   updated_at (string)  Timestamp as an ISO8610 date string, indicating
      when the identified account was last updated.  The RC MAY use this
      value to determine if it needs to request updated profile
      information through an identity API.  The definition of such an
      identity API is out of scope for this specification.











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   "subject": {
      "sub_ids": [ {
        "subject_type": "email",
        "email": "user@example.com",
      } ],
      "assertions": {
        "id_token": "eyj..."
      }
   }

   The AS MUST return the "subject" field only in cases where the AS is
   sure that the RO and the RQ are the same party.  This can be
   accomplished through some forms of interaction with the RO
   (Section 4).

   Subject identifiers returned by the AS SHOULD uniquely identify the
   RO at the AS.  Some forms of subject identifier are opaque to the RC
   (such as the subject of an issuer and subject pair), while others
   forms (such as email address and phone number) are intended to allow
   the RC to correlate the identifier with other account information at
   the RC.  The RC MUST NOT request or use any returned subject
   identifiers for communication purposes (see Section 2.2).  That is, a
   subject identifier returned in the format of an email address or a
   phone number only identifies the RO to the AS and does not indicate
   that the AS has validated that the represented email address or phone
   number in the identifier is suitable for communication with the
   current user.  To get such information, the RC MUST use an identity
   protocol to request and receive additional identity claims.  While
   Section 2.8 specifies one such method, other identity protocols could
   also be used on top of GNAP to convey this information and the
   details of an identity protocol and associated schema are outside the
   scope of this specification.

   [[ See issue #75 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/75) ]]

   [[ See issue #74 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/74) ]]

   Extensions to this specification MAY define additional response
   properties in a registry TBD (Section 12).

3.5.  Returning Dynamically-bound Reference Handles

   Many parts of the RC's request can be passed as either a value or a
   reference.  The use of a reference in place of a value allows for a
   client to optimize requests to the AS.




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   Some references, such as for the RC instance's identity
   (Section 2.3.1) or the requested resources (Section 2.1.2), can be
   managed statically through an admin console or developer portal
   provided by the AS or RS.  The developer of the RC can include these
   values in their code for a more efficient and compact request.

   If desired, the AS MAY also generate and return some of these
   references dynamically to the RC in its response to facilitate
   multiple interactions with the same software.  The RC SHOULD use
   these references in future requests in lieu of sending the associated
   data value.  These handles are intended to be used on future
   requests.

   Dynamically generated handles are string values that MUST be
   protected by the RC as secrets.  Handle values MUST be unguessable
   and MUST NOT contain any sensitive information.  Handle values are
   opaque to the RC.

   [[ See issue #76 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/76) ]]

   All dynamically generated handles are returned as fields in the root
   JSON object of the response.  This specification defines the
   following dynamic handle returns, additional handles can be defined
   in a registry TBD (Section 12).

   instance_id (string)  A string value used to represent the
      information in the "client" object that the RC can use in a future
      request, as described in Section 2.3.1.

   user_handle (string)  A string value used to represent the current
      user.  The RC can use in a future request, as described in
      Section 2.4.1.

   This non-normative example shows two handles along side an issued
   access token.

   {
       "user_handle": "XUT2MFM1XBIKJKSDU8QM",
       "instance_id": "7C7C4AZ9KHRS6X63AJAO",
       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "key": false
       }
   }

   [[ See issue #77 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/77) ]]



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   [[ See issue #78 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/78) ]]

3.6.  Error Response

   If the AS determines that the request cannot be issued for any
   reason, it responds to the RC with an error message.

   error (string)  The error code.

   {

     "error": "user_denied"

   }

   The error code is one of the following, with additional values
   available in a registry TBD (Section 12):

   user_denied  The RO denied the request.

   too_fast  The RC did not respect the timeout in the wait response.

   unknown_request  The request referenced an unknown ongoing access
      request.

   [[ See issue #79 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/79) ]]

3.7.  Extending the Response

   Extensions to this specification MAY define additional fields for the
   grant response in a registry TBD (Section 12).

   [[ See issue #80 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/80) ]]

4.  Interaction at the AS

   If the RC indicates that it is capable of driving interaction with
   the RO in its request (Section 2.5), and the AS determines that
   interaction is required and responds to one or more of the RC's
   interaction modes, the RC SHOULD initiate one of the returned
   interaction modes in the response (Section 3.3).

   When the RO is interacting with the AS, the AS MAY perform whatever
   actions it sees fit, including but not limited to:




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   *  authenticate the current user (who may be the RQ) as the RO

   *  gather consent and authorization from the RO for access to
      requested resources and direct information

   *  allow the RO to modify the parameters of the request (such as
      disallowing some requested resources or specifying an account or
      record)

   *  provide warnings to the RO about potential attacks or negative
      effects of the requested information

   [[ See issue #81 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/81) ]]

4.1.  Interaction at a Redirected URI

   When the RO is directed to the AS through the "redirect"
   (Section 3.3.1) mode, the AS can interact with the RO through their
   web browser to authenticate the user as an RO and gather their
   consent.  Note that since the RC does not add any parameters to the
   URL, the AS MUST determine the grant request being referenced from
   the URL value itself.  If the URL cannot be associated with a
   currently active request, the AS MUST display an error to the RO and
   MUST NOT attempt to redirect the RO back to any RC even if a callback
   is supplied (Section 2.5.3).

   The interaction URL MUST be reachable from the RO's browser, though
   note that the RO MAY open the URL on a separate device from the RC
   itself.  The interaction URL MUST be accessible from an HTTP GET
   request, and MUST be protected by HTTPS or equivalent means.

   With this method, it is common for the RO to be the same party as the
   RQ, since the RC has to communicate the redirection URI to the RQ.

4.2.  Interaction at the User Code URI

   When the RO is directed to the AS through the "user_code"
   (Section 3.3.4) mode, the AS can interact with the RO through their
   web browser to collect the user code, authenticate the user as an RO,
   and gather their consent.  Note that since the URL itself is static,
   the AS MUST determine the grant request being referenced from the
   user code value itself.  If the user code cannot be associated with a
   currently active request, the AS MUST display an error to the RO and
   MUST NOT attempt to redirect the RO back to any RC even if a callback
   is supplied (Section 2.5.3).





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   The user code URL MUST be reachable from the RO's browser, though
   note that the RO MAY open the URL on a separate device from the RC
   itself.  The user code URL MUST be accessible from an HTTP GET
   request, and MUST be protected by HTTPS or equivalent means.

   While it is common for the RO to be the same party as the RQ, since
   the RC has to communicate the user code to someone, there are cases
   where the RQ and RO are separate parties and the authorization
   happens asynchronously.

4.3.  Interaction through an Application URI

   When the RC successfully launches an application through the "app"
   mode (Section 3.3.2), the AS interacts with the RO through that
   application to authenticate the user as the RO and gather their
   consent.  The details of this interaction are out of scope for this
   specification.

   [[ See issue #82 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/82) ]]

4.4.  Post-Interaction Completion

   Upon completing an interaction with the RO, if a "callback"
   (Section 3.3.3) mode is available with the current request, the AS
   MUST follow the appropriate method at the end of interaction to allow
   the RC to continue.  If this mode is not available, the AS SHOULD
   instruct the RO to return to their RC software upon completion.  Note
   that these steps still take place in most error cases, such as when
   the RO has denied access.  This pattern allows the RC to potentially
   recover from the error state without restarting the request from
   scratch by modifying its request or providing additional information
   directly to the AS.

   [[ See issue #83 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/83) ]]

   The AS MUST create an interaction reference and associate that
   reference with the current interaction and the underlying pending
   request.  This value MUST be sufficiently random so as not to be
   guessable by an attacker.  The interaction reference MUST be one-
   time-use.

   The AS MUST calculate a hash value based on the RC and AS nonces and
   the interaction reference, as described in Section 4.4.3.  The RC
   will use this value to validate the return call from the AS.





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   The AS then MUST send the hash and interaction reference based on the
   interaction finalization mode as described in the following sections.

4.4.1.  Completing Interaction with a Browser Redirect to the Callback
        URI

   When using the "callback" interaction mode (Section 3.3.3) with the
   "redirect" method, the AS signals to the RC that interaction is
   complete and the request can be continued by directing the RO (in
   their browser) back to the RC's callback URL sent in the callback
   request (Section 2.5.3.1).

   The AS secures this callback by adding the hash and interaction
   reference as query parameters to the RC's callback URL.

   hash  REQUIRED.  The interaction hash value as described in
      Section 4.4.3.

   interact_ref  REQUIRED.  The interaction reference generated for this
      interaction.

   The means of directing the RO to this URL are outside the scope of
   this specification, but common options include redirecting the RO
   from a web page and launching the system browser with the target URL.

https://client.example.net/return/123455
  ?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
  &interact_ref=4IFWWIKYBC2PQ6U56NL1

   When receiving the request, the RC MUST parse the query parameters to
   calculate and validate the hash value as described in Section 4.4.3.
   If the hash validates, the RC sends a continuation request to the AS
   as described in Section 5.1 using the interaction reference value
   received here.

4.4.2.  Completing Interaction with a Direct HTTP Request Callback

   When using the "callback" interaction mode (Section 3.3.3) with the
   "push" method, the AS signals to the RC that interaction is complete
   and the request can be continued by sending an HTTP POST request to
   the RC's callback URL sent in the callback request (Section 2.5.3.2).

   The entity message body is a JSON object consisting of the following
   two fields:

   hash (string)  REQUIRED.  The interaction hash value as described in
      Section 4.4.3.




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   interact_ref (string)  REQUIRED.  The interaction reference generated
      for this interaction.

POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json

{
  "hash": "p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A",
  "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
}

   When receiving the request, the RC MUST parse the JSON object and
   validate the hash value as described in Section 4.4.3.  If the hash
   validates, the RC sends a continuation request to the AS as described
   in Section 5.1 using the interaction reference value received here.

4.4.3.  Calculating the interaction hash

   The "hash" parameter in the request to the RC's callback URL ties the
   front channel response to an ongoing request by using values known
   only to the parties involved.  This security mechanism allows the RC
   to protect itself against several kinds of session fixation and
   injection attacks.  The AS MUST always provide this hash, and the RC
   MUST validate the hash when received.

   [[ See issue #84 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/84) ]]

   To calculate the "hash" value, the party doing the calculation first
   takes the "nonce" value sent by the RC in the interaction section of
   the initial request (Section 2.5.3), the AS's nonce value from the
   callback response (Section 3.3.3), and the "interact_ref" sent to the
   RC's callback URL.  These three values are concatenated to each other
   in this order using a single newline character as a separator between
   the fields.  There is no padding or whitespace before or after any of
   the lines, and no trailing newline character.

   VJLO6A4CAYLBXHTR0KRO
   MBDOFXG4Y5CVJCX821LH
   4IFWWIKYBC2PQ6U56NL1

   The party then hashes this string with the appropriate algorithm
   based on the "hash_method" parameter of the "callback".  If the
   "hash_method" value is not present in the RC's request, the algorithm
   defaults to "sha3".





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   [[ See issue #56 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/56) ]]

4.4.3.1.  SHA3-512

   The "sha3" hash method consists of hashing the input string with the
   512-bit SHA3 algorithm.  The byte array is then encoded using URL
   Safe Base64 with no padding.  The resulting string is the hash value.

p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A

4.4.3.2.  SHA2-512

   The "sha2" hash method consists of hashing the input string with the
   512-bit SHA2 algorithm.  The byte array is then encoded using URL
   Safe Base64 with no padding.  The resulting string is the hash value.

62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bpj84rh4mC9aE9x7HPBFcIHw

5.  Continuing a Grant Request

   While it is possible for the AS to return a Section 3 with all the
   RC's requested information (including access tokens (Section 3.2) and
   direct user information (Section 3.4)), it's more common that the AS
   and the RC will need to communicate several times over the lifetime
   of an access grant.  This is often part of facilitating interaction
   (Section 4), but it could also be used to allow the AS and RC to
   continue negotiating the parameters of the original grant request
   (Section 2).

   To enable this ongoing negotiation, the AS returns a "continue" field
   in the response (Section 3.1) that contains information the RC needs
   to continue this process with another request, including a URI to
   access as well as an optional access token to use during the
   continued requests.

   When the RC makes any calls to the continuation URL, the RC MUST
   present proof of the most recent key associated with this ongoing
   request by signing the request as described in Section 8.  The key in
   use will be either the key from the initial request (Section 2.3.2)
   or its most recent rotation.  [[ See issue #85 (https://github.com/
   ietf-wg-gnap/gnap-core-protocol/issues/85) ]]

   For example, here the RC makes a POST request and signs with detached
   JWS:






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   POST /continue/80UPRY5NM33OMUKMKSKU HTTP/1.1
   Host: server.example.com
   Detached-JWS: ejy0...

   If the AS includes an "access_token" in the "continue" response in
   Section 3.1, the RC MUST include the access token the request as
   described in Section 7.  Note that the access token is always bound
   to the RC's presented key (or its most recent rotation).

   For example, here the RC makes a POST request with the interaction
   reference, includes the access token, and signs with detached JWS:

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   {
     "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

   The AS MUST be able to tell from the RC's request which specific
   ongoing request is being accessed.  Common methods for doing so
   include using a unique, unguessable URL for each continuation
   response, associating the request with the provided access token, or
   allowing only a single ongoing grant request for a given RC instance
   at a time.  If the AS cannot determine a single active grant request
   to map the continuation request to, the AS MUST return an error.

   The ability to continue an already-started request allows the RC to
   perform several important functions, including presenting additional
   information from interaction, modifying the initial request, and
   getting the current state of the request.

   If a "wait" parameter was included in the continuation response
   (Section 3.1), the RC MUST NOT call the continuation URI prior to
   waiting the number of seconds indicated.  If no "wait" period is
   indicated, the RC SHOULD wait at least 5 seconds If the RC does not
   respect the given wait period, the AS MUST return an error. [[ See
   issue #86 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/86) ]]

   The response from the AS is a JSON object and MAY contain any of the
   fields described in Section 3, as described in more detail in the
   sections below.





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   If the AS determines that the RC can make a further continuation
   request, the AS MUST include a new "continue" response (Section 3.1).
   If the continuation was previously bound to an access token, the new
   "continue" response MUST include a bound access token as well, and
   this token SHOULD be a new access token.  If the AS does not return a
   new "continue" response, the RC MUST NOT make an additional
   continuation request.  If a RC does so, the AS MUST return an error.
   [[ See issue #87 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/87) ]]

   For continuation functions that require the RC to send a message
   body, the body MUST be a JSON object.

5.1.  Continuing After a Completed Interaction

   When the AS responds to the RC's "callback" parameter as in
   Section 4.4.1, this response includes an interaction reference.  The
   RC MUST include that value as the field "interact_ref" in a POST
   request to the continuation URI.

   POST /continue/80UPRY5NM33OMUKMKSKU HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
     "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

   Since the interaction reference is a one-time-use value as described
   in Section 4.4.1, if the RC needs to make additional continuation
   calls after this request, the RC MUST NOT include the interaction
   reference.  If the AS detects an RC submitting the same interaction
   reference multiple times, the AS MUST return an error and SHOULD
   invalidate the ongoing request.

   The Section 3 MAY contain any newly-created access tokens
   (Section 3.2) or newly-released subject claims (Section 3.4).  The
   response MAY contain a new "continue" response (Section 3.1) as
   described above.  The response SHOULD NOT contain any interaction
   responses (Section 3.3). [[ See issue #89 (https://github.com/ietf-
   wg-gnap/gnap-core-protocol/issues/89) ]]

   For example, if the request is successful in causing the AS to issue
   access tokens and release subject claims, the response could look
   like this:





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{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "subject": {
        "sub_ids": [ {
           "subject_type": "email",
           "email": "user@example.com",
        } ]
    }
}

   With this example, the RC can not make an additional continuation
   request because a "continue" field is not included.

   [[ See issue #88 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/88) ]]

5.2.  Continuing During Pending Interaction

   When the RC does not include a "callback" parameter, the RC will
   often need to poll the AS until the RO has authorized the request.
   To do so, the RC makes a POST request to the continuation URI as in
   Section 5.1, but does not include a message body.

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   The Section 3 MAY contain any newly-created access tokens
   (Section 3.2) or newly-released subject claims (Section 3.4).  The
   response MAY contain a new "continue" response (Section 3.1) as
   described above.  If a "continue" field is included, it SHOULD
   include a "wait" field to facilitate a reasonable polling rate by the
   RC.  The response SHOULD NOT contain interaction responses
   (Section 3.3).

   For example, if the request has not yet been authorized by the RO,
   the AS could respond by telling the RC to make another continuation
   request in the future.  In this example, a new, unique access token
   has been issued for the call, which the RC will use in its next
   continuation request.





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   {
       "continue": {
           "access_token": {
               "value": "33OMUKMKSKU80UPRY5NM",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 30
       }
   }

   [[ See issue #90 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/90) ]]

   [[ See issue #91 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/91) ]]

   If the request is successful in causing the AS to issue access tokens
   and release subject claims, the response could look like this
   example:

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "subject": {
        "sub_ids": [ {
           "subject_type": "email",
           "email": "user@example.com",
        } ]
    }
}

5.3.  Modifying an Existing Request

   The RC might need to modify an ongoing request, whether or not tokens
   have already been issued or claims have already been released.  In
   such cases, the RC makes an HTTP PATCH request to the continuation
   URI and includes any fields it needs to modify.  Fields that aren't
   included in the request are considered unchanged from the original
   request.

   The RC MAY include the "resources" and "subject" fields as described
   in Section 2.1 and Section 2.2.  Inclusion of these fields override
   any values in the initial request, which MAY trigger additional
   requirements and policies by the AS.  For example, if the RC is



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   asking for more access, the AS could require additional interaction
   with the RO to gather additional consent.  If the RC is asking for
   more limited access, the AS could determine that sufficient
   authorization has been granted to the RC and return the more limited
   access rights immediately.  [[ See issue #92 (https://github.com/
   ietf-wg-gnap/gnap-core-protocol/issues/92) ]]

   The RC MAY include the "interact" field as described in Section 2.5.
   Inclusion of this field indicates that the RC is capable of driving
   interaction with the RO, and this field replaces any values from a
   previous request.  The AS MAY respond to any of the interaction
   responses as described in Section 3.3, just like it would to a new
   request.

   The RC MAY include the "user" field as described in Section 2.4 to
   present new assertions or information about the RQ.  [[ See issue #93
   (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/93) ]]

   The RC MUST NOT include the "client" section of the request. [[ See
   issue #94 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/94) ]]

   The RC MAY include post-interaction responses such as described in
   Section 5.1. [[ See issue #95 (https://github.com/ietf-wg-gnap/gnap-
   core-protocol/issues/95) ]]

   Modification requests MUST NOT alter previously-issued access tokens.
   Instead, any access tokens issued from a continuation are considered
   new, separate access tokens.  The AS MAY revoke existing access
   tokens after a modification has occurred.  [[ See issue #96
   (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/96) ]]

   If the modified request can be granted immediately by the AS, the
   Section 3 MAY contain any newly-created access tokens (Section 3.2)
   or newly-released subject claims (Section 3.4).  The response MAY
   contain a new "continue" response (Section 3.1) as described above.
   If interaction can occur, the response SHOULD contain interaction
   responses (Section 3.3) as well.

   For example, an RC initially requests a set of resources using
   references:










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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "read", "write"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "client": "987YHGRT56789IOLK"
   }

   Access is granted by the RO, and a token is issued by the AS.  In its
   final response, the AS includes a "continue" field:

   {
       "continue": {
           "access_token": {
               "value": "80UPRY5NM33OMUKMKSKU",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 30
       },
       "access_token": ...
   }

   This allows the RC to make an eventual continuation call.  The RC
   realizes that it no longer needs "write" access and therefore
   modifies its ongoing request, here asking for just "read" access
   instead of both "read" and "write" as before.












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   PATCH /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   {
       "resources": [
           "read"
       ]
       ...
   }

   The AS replaces the previous "resources" from the first request,
   allowing the AS to determine if any previously-granted consent
   already applies.  In this case, the AS would likely determine that
   reducing the breadth of the requested access means that new access
   tokens can be issued to the RC.  The AS would likely revoke
   previously-issued access tokens that had the greater access rights
   associated with them.

   {
       "continue": {
           "access_token": {
               "value": "M33OMUK80UPRY5NMKSKU",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 30
       },
       "access_token": ...
   }

   For another example, the RC initially requests read-only access but
   later needs to step up its access.  The initial request could look
   like this example.















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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "read"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "client": "987YHGRT56789IOLK"
   }

   Access is granted by the RO, and a token is issued by the AS.  In its
   final response, the AS includes a "continue" field:

   {
       "continue": {
           "access_token": {
               "value": "80UPRY5NM33OMUKMKSKU",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 30
       },
       "access_token": ...
   }

   This allows the RC to make an eventual continuation call.  The RC
   later realizes that it now needs "write" access in addition to the
   "read" access.  Since this is an expansion of what it asked for
   previously, the RC also includes a new interaction section in case
   the AS needs to interact with the RO again to gather additional
   authorization.  Note that the RC's nonce and callback are different
   from the initial request.  Since the original callback was already
   used in the initial exchange, and the callback is intended for one-
   time-use, a new one needs to be included in order to use the callback
   again.

   [[ See issue #97 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/97) ]]



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   PATCH /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   {
       "resources": [
           "read", "write"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/654321",
               "nonce": "K82FX4T4LKLTI25DQFZC"
           }
       }
   }

   From here, the AS can determine that the RC is asking for more than
   it was previously granted, but since the RC has also provided a
   mechanism to interact with the RO, the AS can use that to gather the
   additional consent.  The protocol continues as it would with a new
   request.  Since the old access tokens are good for a subset of the
   rights requested here, the AS might decide to not revoke them.
   However, any access tokens granted after this update process are new
   access tokens and do not modify the rights of existing access tokens.

5.4.  Getting the Current State of a Grant Request

   If the RC needs to get the current state of an ongoing grant request,
   it makes an HTTP GET request to the continuation URI.  This request
   MUST NOT alter the grant request in any fashion, including causing
   the issuance of new access tokens or modification of interaction
   parameters.

   The AS MAY include existing access tokens and previously-released
   subject claims in the response.  The AS MUST NOT issue a new access
   token or release a new subject claim in response to this request.

   GET /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...





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   The response MAY include any fields described Section 3 that are
   applicable to this ongoing request, including the most recently
   issued access tokens, any released subject claims, and any currently
   active interaction modes.  The response MAY contain a new "continue"
   response (Section 3.1) as described above.

   [[ See issue #98 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/98) ]]

5.5.  Canceling a Grant Request

   If the RC wishes to cancel an ongoing grant request, it makes an HTTP
   DELETE request to the continuation URI.

   DELETE /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   If the request is successfully cancelled, the AS responds with an
   HTTP 202.  The AS MUST revoke all associated access tokens, if
   possible.

6.  Token Management

   If an access token response includes the "manage" parameter as
   described in Section 3.2.1, the RC MAY call this URL to manage the
   access token with any of the actions defined in the following
   sections.  Other actions are undefined by this specification.

   The access token being managed acts as the access element for its own
   management API.  The RC MUST present proof of an appropriate key
   along with the access token.

   If the token is sender-constrained (i.e., not a bearer token), it
   MUST be sent with the appropriate binding for the access token
   (Section 7).

   If the token is a bearer token, the RC MUST present proof of the same
   key identified in the initial request (Section 2.3.2) as described in
   Section 8.

   The AS MUST validate the proof and assure that it is associated with
   either the token itself or the RC the token was issued to, as
   appropriate for the token's presentation type.





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   [[ See issue #99 (https://github.com/ietf-wg-gnap/gnap-core-protocol/
   issues/99) ]]

6.1.  Rotating the Access Token

   The RC makes an HTTP POST to the token management URI, sending the
   access token in the appropriate header and signing the request with
   the appropriate key.

   POST /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
   Host: server.example.com
   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....

   [[ See issue #100 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/100) ]]

   The AS validates that the token presented is associated with the
   management URL, that the AS issued the token to the given RC, and
   that the presented key is appropriate to the token.

   If the access token has expired, the AS SHOULD honor the rotation
   request to the token management URL since it is likely that the RC is
   attempting to refresh the expired token.  To support this, the AS MAY
   apply different lifetimes for the use of the token in management vs.
   its use at an RS.  An AS MUST NOT honor a rotation request for an
   access token that has been revoked, either by the AS or by the RC
   through the token management URI (Section 6.2).

   If the token is validated and the key is appropriate for the request,
   the AS MUST invalidate the current access token associated with this
   URL, if possible, and return a new access token response as described
   in Section 3.2.1, unless the "multi_token" flag is specified in the
   request.  The value of the access token MUST NOT be the same as the
   current value of the access token used to access the management API.
   The response MAY include an updated access token management URL as
   well, and if so, the RC MUST use this new URL to manage the new
   access token. [[ See issue #101 (https://github.com/ietf-wg-gnap/
   gnap-core-protocol/issues/101) ]]

   [[ See issue #102 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/102) ]]









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{
    "access_token": {
        "value": "FP6A8H6HY37MH13CK76LBZ6Y1UADG6VEUPEER5H2",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            {
                "type": "photo-api",
                "actions": [
                    "read",
                    "write",
                    "dolphin"
                ],
                "locations": [
                    "https://server.example.net/",
                    "https://resource.local/other"
                ],
                "datatypes": [
                    "metadata",
                    "images"
                ]
            },
            "read", "dolphin-metadata"
        ]
    }
}

   [[ See issue #103 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/103) ]]

6.2.  Revoking the Access Token

   If the RC wishes to revoke the access token proactively, such as when
   a user indicates to the RC that they no longer wish for it to have
   access or the RC application detects that it is being uninstalled,
   the RC can use the token management URI to indicate to the AS that
   the AS should invalidate the access token for all purposes.

   The RC makes an HTTP DELETE request to the token management URI,
   presenting the access token and signing the request with the
   appropriate key.

   DELETE /token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L HTTP/1.1
   Host: server.example.com
   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....





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   If the key presented is associated with the token (or the RC, in the
   case of a bearer token), the AS MUST invalidate the access token, if
   possible, and return an HTTP 204 response code.

   204 No Content

   Though the AS MAY revoke an access token at any time for any reason,
   the token management function is specifically for the RC's use.  If
   the access token has already expired or has been revoked through
   other means, the AS SHOULD honor the revocation request to the token
   management URL as valid, since the end result is still the token not
   being usable.

7.  Using Access Tokens

   The method the RC uses to send an access token to the RS depends on
   the value of the "key" and "proof" parameters in the access token
   response (Section 3.2.1).

   If the key value is the boolean "false", the access token is a bearer
   token sent using the HTTP Header method defined in [RFC6750].

   Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0

   The form parameter and query parameter methods of [RFC6750] MUST NOT
   be used.

   If the "key" value is the boolean "true", the access token MUST be
   sent to the RS using the same key and proofing mechanism that the RC
   used in its initial request.

   If the "key" value is an object, the value of the "proof" field
   within the key indicates the particular proofing mechanism to use.
   The access token is sent using the HTTP authorization scheme "GNAP"
   along with a key proof as described in Section 8 for the key bound to
   the access token.  For example, a "jwsd"-bound access token is sent
   as follows:

   Authorization: GNAP OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0
   Detached-JWS: eyj0....

   [[ See issue #104 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/104) ]]








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8.  Binding Keys

   Any keys presented by the RC to the AS or RS MUST be validated as
   part of the request in which they are presented.  The type of binding
   used is indicated by the proof parameter of the key section in the
   initial request Section 2.3.2.  Values defined by this specification
   are as follows:

   jwsd  A detached JWS signature header

   jws  Attached JWS payload

   mtls  Mutual TLS certificate verification

   dpop  OAuth Demonstration of Proof-of-Possession key proof header

   httpsig  HTTP Signing signature header

   oauthpop  OAuth PoP key proof authentication header

   Additional proofing methods are defined by a registry TBD
   (Section 12).

   All key binding methods used by this specification MUST cover all
   relevant portions of the request, including anything that would
   change the nature of the request, to allow for secure validation of
   the request by the AS.  Relevant aspects include the URI being
   called, the HTTP method being used, any relevant HTTP headers and
   values, and the HTTP message body itself.  The recipient of the
   signed message MUST validate all components of the signed message to
   ensure that nothing has been tampered with or substituted in a way
   that would change the nature of the request.

   When used for delegation in GNAP, these key binding mechanisms allow
   the AS to ensure that the keys presented by the RC in the initial
   request are in control of the party calling any follow-up or
   continuation requests.  To facilitate this requirement, all keys in
   the initial request Section 2.3.2 MUST be proved in all continuation
   requests Section 5 and token management requests Section 6, modulo
   any rotations on those keys over time that the AS knows about.  The
   AS MUST validate all keys presented by the RC (Section 2.3.2) or
   referenced in an ongoing request for each call within that request.

   [[ See issue #105 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/105) ]]

   When used to bind to an access token, the access token MUST be
   covered by the signature method.



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8.1.  Detached JWS

   This method is indicated by "jwsd" in the "proof" field.  A JWS
   [RFC7515] signature object is created as follows:

   The header of the JWS MUST contain the "kid" field of the key bound
   to this RC for this request.  The JWS header MUST contain an "alg"
   field appropriate for the key identified by kid and MUST NOT be
   "none".  The "b64" field MUST be set to "false" and the "crit" field
   MUST contain at least "b64" as specified in [RFC7797]

   To protect the request, the JWS header MUST contain the following
   additional fields.

   htm (string)  The HTTP Method used to make this request, as an
      uppercase ASCII string.

   htu (string)  The HTTP URI used for this request, including all path
      and query components.

   ts (integer)  A timestamp of the request in integer seconds

   at_hash (string)  When to bind a request to an access token, the
      access token hash value.  Its value is the base64url encoding of
      the left-most half of the hash of the octets of the ASCII
      representation of the "access_token" value, where the hash
      algorithm used is the hash algorithm used in the "alg" header
      parameter of the JWS's JOSE Header.  For instance, if the "alg" is
      "RS256", hash the "access_token" value with SHA-256, then take the
      left-most 128 bits and base64url encode them.

   [[ See issue #106 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/106) ]]

   The payload of the JWS object is the serialized body of the request,
   and the object is signed according to detached JWS [RFC7797].

   The RC presents the signature in the Detached-JWS HTTP Header field.
   [[ See issue #107 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/107) ]]











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  POST /tx HTTP/1.1
  Host: server.example.com
  Content-Type: application/json
  Detached-JWS: eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.
    .Y287HMtaY0EegEjoTd_04a4GC6qV48GgVbGKOhHdJnDtD0VuUlVjLfwne8AuUY3U7e8
    9zUWwXLnAYK_BiS84M8EsrFvmv8yDLWzqveeIpcN5_ysveQnYt9Dqi32w6IOtAywkNUD
    ZeJEdc3z5s9Ei8qrYFN2fxcu28YS4e8e_cHTK57003WJu-wFn2TJUmAbHuqvUsyTb-nz
    YOKxuCKlqQItJF7E-cwSb_xULu-3f77BEU_vGbNYo5ZBa2B7UHO-kWNMSgbW2yeNNLbL
    C18Kv80GF22Y7SbZt0e2TwnR2Aa2zksuUbntQ5c7a1-gxtnXzuIKa34OekrnyqE1hmVW
    peQ

  {
      "resources": [
          "dolphin-metadata"
      ],
      "interact": {
          "redirect": true,
          "callback": {
              "method": "redirect",
              "uri": "https://client.foo",
              "nonce": "VJLO6A4CAYLBXHTR0KRO"
          }
      },
      "client": {
        "proof": "jwsd",
        "key": {
          "jwk": {
                      "kty": "RSA",
                      "e": "AQAB",
                      "kid": "xyz-1",
                      "alg": "RS256",
                      "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8
  xYJCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPF
  vpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyD
  SWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS
  63WYPHi_Ap2B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFe
  kpdfWdiPQddQ6Y1cK2U3obvUg7w"
          }
        }
        "display": {
          "name": "My Client Display Name",
          "uri": "https://example.net/client"
        },
      }
  }






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   If the request being made does not have a message body, such as an
   HTTP GET, OPTIONS, or DELETE method, the JWS signature is calculated
   over an empty payload.

   When the server (AS or RS) receives the Detached-JWS header, it MUST
   parse its contents as a detached JWS object.  The HTTP Body is used
   as the payload for purposes of validating the JWS, with no
   transformations.

   [[ See issue #108 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/108) ]]

8.2.  Attached JWS

   This method is indicated by "jws" in the "proof" field.  A JWS
   [RFC7515] signature object is created as follows:

   The header of the JWS MUST contain the "kid" field of the key bound
   to this RC for this request.  The JWS header MUST contain an "alg"
   field appropriate for the key identified by kid and MUST NOT be
   "none".

   To protect the request, the JWS header MUST contain the following
   additional fields.

   htm (string)  The HTTP Method used to make this request, as an
      uppercase ASCII string.

   htu (string)  The HTTP URI used for this request, including all path
      and query components.

   ts (integer)  A timestamp of the request in integer seconds

   at_hash (string)  When to bind a request to an access token, the
      access token hash value.  Its value is the base64url encoding of
      the left-most half of the hash of the octets of the ASCII
      representation of the "access_token" value, where the hash
      algorithm used is the hash algorithm used in the "alg" header
      parameter of the JWS's JOSE Header.  For instance, if the "alg" is
      "RS256", hash the "access_token" value with SHA-256, then take the
      left-most 128 bits and base64url encode them.

   [[ See issue #107 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/107) ]]

   The payload of the JWS object is the JSON serialized body of the
   request, and the object is signed according to JWS and serialized
   into compact form [RFC7515].



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   The RC presents the JWS as the body of the request along with a
   content type of "application/jose".  The AS MUST extract the payload
   of the JWS and treat it as the request body for further processing.

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-Type: application/jose

   eyJhbGciOiJSUzI1NiIsImtpZCI6IktBZ05wV2JSeXk5T
   WYycmlrbDQ5OExUaE1ydmtiWldIVlNRT0JDNFZIVTQiLC
   JodG0iOiJwb3N0IiwiaHR1IjoiL3R4IiwidHMiOjE2MDM
   4MDA3ODN9.eyJjYXBhYmlsaXRpZXMiOltdLCJjbGllbnQ
   iOnsia2V5Ijp7Imp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
   QVFBQiIsImtpZCI6IktBZ05wV2JSeXk5TWYycmlrbDQ5O
   ExUaE1ydmtiWldIVlNRT0JDNFZIVTQiLCJuIjoibGxXbU
   hGOFhBMktOTGRteE9QM2t4RDlPWTc2cDBTcjM3amZoejk
   0YTkzeG0yRk5xb1NQY1JaQVBkMGxxRFM4TjNVaWE1M2RC
   MjNaNTlPd1k0YnBNX1ZmOEdKdnZwdExXbnhvMVB5aG1Qc
   i1lY2RTQ1JRZFRjX1pjTUY0aFJWNDhxcWx2dUQwbXF0Y0
   RiSWtTQkR2Y2NKbVpId2ZUcERIaW5UOHR0dmNWUDhWa0F
   NQXE0a1ZhenhPcE1vSVJzb3lFcF9lQ2U1cFN3cUhvMGRh
   Q1dOS1ItRXBLbTZOaU90ZWRGNE91bXQ4TkxLVFZqZllnR
   khlQkRkQ2JyckVUZDR2Qk13RHRBbmpQcjNDVkN3d3gyYk
   FRVDZTbHhGSjNmajJoaHlJcHE3cGM4clppYjVqTnlYS3d
   mQnVrVFZZWm96a3NodC1Mb2h5QVNhS3BZVHA4THROWi13
   In0sInByb29mIjoiandzIn0sIm5hbWUiOiJNeSBGaXN0I
   ENsaWVudCIsInVyaSI6Imh0dHA6Ly9sb2NhbGhvc3QvY2
   xpZW50L2NsaWVudElEIn0sImludGVyYWN0Ijp7ImNhbGx
   iYWNrIjp7Im1ldGhvZCI6InJlZGlyZWN0Iiwibm9uY2Ui
   OiJkOTAyMTM4ODRiODQwOTIwNTM4YjVjNTEiLCJ1cmkiO
   iJodHRwOi8vbG9jYWxob3N0L2NsaWVudC9yZXF1ZXN0LW
   RvbmUifSwicmVkaXJlY3QiOnRydWV9LCJyZXNvdXJjZXM
   iOnsiYWN0aW9ucyI6WyJyZWFkIiwicHJpbnQiXSwibG9j
   YXRpb25zIjpbImh0dHA6Ly9sb2NhbGhvc3QvcGhvdG9zI
   l0sInR5cGUiOiJwaG90by1hcGkifSwic3ViamVjdCI6ey
   JzdWJfaWRzIjpbImlzcy1zdWIiLCJlbWFpbCJdfX0.LUy
   Z8_fERmxbYARq8kBYMwzcd8GnCAKAlo2ZSYLRRNAYWPrp
   2XGLJOvg97WK1idf_LB08OJmLVsCXxCvn9mgaAkYNL_Zj
   HcusBvY1mNo0E1sdTEr31CVKfC-6WrZCscb8YqE4Ayhh0
   Te8kzSng3OkLdy7xN4xeKuHzpF7yGsM52JZ0cBcTo6WrY
   EfGdr08AWQJ59ht72n3jTsmYNy9A6I4Wrvfgj3TNxmwYo
   jpBAicfjnzA1UVcNm9F_xiSz1_y2tdH7j5rVqBMQife-k
   9Ewk95vr3lurthenliYSNiUinVfoW1ybnaIBcTtP1_YCx
   g_h1y-B5uZEvYNGCuoCqa6IQ

   This example's JWS header decodes to:





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   {
     "alg": "RS256",
     "kid": "KAgNpWbRyy9Mf2rikl498LThMrvkbZWHVSQOBC4VHU4",
     "htm": "post",
     "htu": "/tx",
     "ts": 1603800783
   }

   And the JWS body decodes to:










































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   {
     "capabilities": [],
     "client": {
       "key": {
         "jwk": {
           "kty": "RSA",
           "e": "AQAB",
           "kid": "KAgNpWbRyy9Mf2rikl498LThMrvkbZWHVSQOBC4VHU4",
           "n": "llWmHF8XA2KNLdmxOP3kxD9OY76p0Sr37jfhz94a93xm2FNqoSPc
           RZAPd0lqDS8N3Uia53dB23Z59OwY4bpM_Vf8GJvvptLWnxo1PyhmPr-ecd
           SCRQdTc_ZcMF4hRV48qqlvuD0mqtcDbIkSBDvccJmZHwfTpDHinT8ttvcV
           P8VkAMAq4kVazxOpMoIRsoyEp_eCe5pSwqHo0daCWNKR-EpKm6NiOtedF4
           Oumt8NLKTVjfYgFHeBDdCbrrETd4vBMwDtAnjPr3CVCwwx2bAQT6SlxFJ3
           fj2hhyIpq7pc8rZib5jNyXKwfBukTVYZozksht-LohyASaKpYTp8LtNZ-w"
         },
         "proof": "jws"
       },
       "name": "My Fist Client",
       "uri": "http://localhost/client/clientID"
     },
     "interact": {
       "callback": {
         "method": "redirect",
         "nonce": "d90213884b840920538b5c51",
         "uri": "http://localhost/client/request-done"
       },
       "redirect": true
     },
     "resources": {
       "actions": [
         "read",
         "print"
       ],
       "locations": [
         "http://localhost/photos"
       ],
       "type": "photo-api"
     },
     "subject": {
       "sub_ids": [
         "iss_sub",
         "email"
       ]
     }
   }






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   If the request being made does not have a message body, such as an
   HTTP GET, OPTIONS, or DELETE method, the JWS signature is calculated
   over an empty payload and passed in the "Detached-JWS" header as
   described in Section 8.1.

   [[ See issue #109 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/109) ]]

8.3.  Mutual TLS

   This method is indicated by "mtls" in the "proof" field.  The RC
   presents its client certificate during TLS negotiation with the
   server (either AS or RS).  The AS or RS takes the thumbprint of the
   client certificate presented during mutual TLS negotiation and
   compares that thumbprint to the thumbprint presented by the RC
   application as described in [RFC8705] section 3.

POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
SSL_CLIENT_CERT: MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3MDUGA1UEAwwuQmVz
 cG9rZSBFbmdpbmVlcmluZyBSb290IENlcnRpZmljYXRlIEF1dGhvcml0eTELMAkG
 A1UECAwCTUExCzAJBgNVBAYTAlVTMRkwFwYJKoZIhvcNAQkBFgpjYUBic3BrLmlv
 MRwwGgYDVQQKDBNCZXNwb2tlIEVuZ2luZWVyaW5nMQwwCgYDVQQLDANNVEkwHhcN
 MTkwNDEwMjE0MDI5WhcNMjQwNDA4MjE0MDI5WjB8MRIwEAYDVQQDDAlsb2NhbGhv
 c3QxCzAJBgNVBAgMAk1BMQswCQYDVQQGEwJVUzEgMB4GCSqGSIb3DQEJARYRdGxz
 Y2xpZW50QGJzcGsuaW8xHDAaBgNVBAoME0Jlc3Bva2UgRW5naW5lZXJpbmcxDDAK
 BgNVBAsMA01USTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMmaXQHb
 s/wc1RpsQ6Orzf6rN+q2ijaZbQxD8oi+XaaN0P/gnE13JqQduvdq77OmJ4bQLokq
 sd0BexnI07Njsl8nkDDYpe8rNve5TjyUDCfbwgS7U1CluYenXmNQbaYNDOmCdHww
 UjV4kKREg6DGAx22Oq7+VHPTeeFgyw4kQgWRSfDENWY3KUXJlb/vKR6lQ+aOJytk
 vj8kVZQtWupPbvwoJe0na/ISNAOhL74w20DWWoDKoNltXsEtflNljVoi5nqsmZQc
 jfjt6LO0T7O1OX3Cwu2xWx8KZ3n/2ocuRqKEJHqUGfeDtuQNt6Jz79v/OTr8puLW
 aD+uyk6NbtGjoQsCAwEAAaOBiTCBhjAJBgNVHRMEAjAAMAsGA1UdDwQEAwIF4DBs
 BgNVHREEZTBjgglsb2NhbGhvc3SCD3Rsc2NsaWVudC5sb2NhbIcEwKgBBIERdGxz
 Y2xpZW50QGJzcGsuaW+GF2h0dHA6Ly90bHNjbGllbnQubG9jYWwvhhNzc2g6dGxz
 Y2xpZW50LmxvY2FsMA0GCSqGSIb3DQEBCwUAA4IBAQCKKv8WlLrT4Z5NazaUrYtl
 TF+2v0tvZBQ7qzJQjlOqAcvxry/d2zyhiRCRS/v318YCJBEv4Iq2W3I3JMMyAYEe
 2573HzT7rH3xQP12yZyRQnetdiVM1Z1KaXwfrPDLs72hUeELtxIcfZ0M085jLboX
 hufHI6kqm3NCyCCTihe2ck5RmCc5l2KBO/vAHF0ihhFOOOby1v6qbPHQcxAU6rEb
 907/p6BW/LV1NCgYB1QtFSfGxowqb9FRIMD2kvMSmO0EMxgwZ6k6spa+jk0IsI3k
 lwLW9b+Tfn/daUbIDctxeJneq2anQyU2znBgQl6KILDSF4eaOqlBut/KNZHHazJh

{
    "resources": [
        "dolphin-metadata"
    ],
    "interact": {



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        "redirect": true,
        "callback": {
            "method": "redirect",
            "uri": "https://client.foo",
            "nonce": "VJLO6A4CAYLBXHTR0KRO"
        }
    },
    "client": {
      "display": {
        "name": "My Client Display Name",
        "uri": "https://example.net/client"
      },
      "key": {
        "proof": "mtls",
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3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"
    }
}

   [[ See issue #110 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/110) ]]










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8.4.  Demonstration of Proof-of-Possession (DPoP)

   This method is indicated by "dpop" in the "proof" field.  The RC
   creates a Demonstration of Proof-of-Possession signature header as
   described in [I-D.ietf-oauth-dpop] section 2.  In addition to the
   required fields, the DPoP body MUST also contain a digest of the
   request body:

   digest (string)  Digest of the request body as the value of the
      Digest header defined in [RFC3230].

 POST /tx HTTP/1.1
 Host: server.example.com
 Content-Type: application/json
 DPoP: eyJ0eXAiOiJkcG9wK2p3dCIsImFsZyI6IlJTMjU2IiwiandrIjp7Imt0eSI6Il
 JTQSIsImUiOiJBUUFCIiwia2lkIjoieHl6LWNsaWVudCIsImFsZyI6IlJTMjU2Iiwibi
 I6Inp3Q1RfM2J4LWdsYmJIcmhlWXBZcFJXaVk5SS1uRWFNUnBablJySWpDczZiX2VteV
 RrQmtEREVqU3lzaTM4T0M3M2hqMS1XZ3hjUGRLTkdaeUlvSDNRWmVuMU1LeXloUXBMSk
 cxLW9MTkxxbTdwWFh0ZFl6U2RDOU8zLW9peXk4eWtPNFlVeU5aclJSZlBjaWhkUUNiT1
 9PQzhRdWdtZzlyZ05ET1NxcHBkYU5lYXMxb3Y5UHhZdnhxcnoxLThIYTdna0QwMFlFQ1
 hIYUIwNXVNYVVhZEhxLU9fV0l2WVhpY2c2STVqNlM0NFZOVTY1VkJ3dS1BbHluVHhRZE
 1BV1AzYll4VlZ5NnAzLTdlVEpva3ZqWVRGcWdEVkRaOGxVWGJyNXlDVG5SaG5oSmd2Zj
 NWakRfbWFsTmU4LXRPcUs1T1NEbEhUeTZnRDlOcWRHQ20tUG0zUSJ9fQ.eyJodHRwX21
 ldGhvZCI6IlBPU1QiLCJodHRwX3VyaSI6Imh0dHA6XC9cL2hvc3QuZG9ja2VyLmludGV
 ybmFsOjk4MzRcL2FwaVwvYXNcL3RyYW5zYWN0aW9uIiwiaWF0IjoxNTcyNjQyNjEzLCJ
 qdGkiOiJIam9IcmpnbTJ5QjR4N2pBNXl5RyJ9.aUhftvfw2NoW3M7durkopReTvONng1
 fOzbWjAlKNSLL0qIwDgfG39XUyNvwQ23OBIwe6IuvTQ2UBBPklPAfJhDTKd8KHEAfidN
 B-LzUOzhDetLg30yLFzIpcEBMLCjb0TEsmXadvxuNkEzFRL-Q-QCg0AXSF1h57eAqZV8
 SYF4CQK9OUV6fIWwxLDd3cVTx83MgyCNnvFlG_HDyim1Xx-rxV4ePd1vgDeRubFb6QWj
 iKEO7vj1APv32dsux67gZYiUpjm0wEZprjlG0a07R984KLeK1XPjXgViEwEdlirUmpVy
 T9tyEYqGrTfm5uautELgMls9sgSyE929woZ59elg

 {
     "resources": [
         "dolphin-metadata"
     ],
     "interact": {
         "redirect": true,
         "callback": {
             "method": "redirect",
             "uri": "https://client.foo",
             "nonce": "VJLO6A4CAYLBXHTR0KRO"
         }
     },
     "client": {
       "display": {
         "name": "My Client Display Name",
         "uri": "https://example.net/client"



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       },
       "proof": "dpop",
       "key": {
         "jwk": {
                     "kty": "RSA",
                     "e": "AQAB",
                     "kid": "xyz-1",
                     "alg": "RS256",
                     "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xYJ
 CCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPFvpkTM
 8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCH
 e5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2
 B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6Y
 1cK2U3obvUg7w"
         }
       }
     }
 }

   [[ See issue #111 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/111) ]]

8.5.  HTTP Signing

   This method is indicated by "httpsig" in the "proof" field.  The RC
   creates an HTTP Signature header as described in
   [I-D.ietf-httpbis-message-signatures] section 4.  The RC MUST
   calculate and present the Digest header as defined in [RFC3230] and
   include this header in the signature.

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-Type: application/json
   Content-Length: 716
   Signature: keyId="xyz-client", algorithm="rsa-sha256",
    headers="(request-target) digest content-length",
    signature="TkehmgK7GD/z4jGkmcHS67cjVRgm3zVQNlNrrXW32Wv7d
   u0VNEIVI/dMhe0WlHC93NP3ms91i2WOW5r5B6qow6TNx/82/6W84p5jqF
   YuYfTkKYZ69GbfqXkYV9gaT++dl5kvZQjVk+KZT1dzpAzv8hdk9nO87Xi
   rj7qe2mdAGE1LLc3YvXwNxuCQh82sa5rXHqtNT1077fiDvSVYeced0UEm
   rWwErVgr7sijtbTohC4FJLuJ0nG/KJUcIG/FTchW9rd6dHoBnY43+3Dzj
   CIthXpdH5u4VX3TBe6GJDO6Mkzc6vB+67OWzPwhYTplUiFFV6UZCsDEeu
   Sa/Ue1yLEAMg=="]}
   Digest: SHA=oZz2O3kg5SEFAhmr0xEBbc4jEfo=

   {
       "resources": [
           "dolphin-metadata"



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       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "push",
               "uri": "https://client.foo",
               "nonce": "VJLO6A4CAYLBXHTR0KRO"
           }
       },
       "client": {
         "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
         },
         "proof": "httpsig",
         "key": {
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
   tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
   y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-
   ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
   06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
   bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
   Y1cK2U3obvUg7w"
           }
         }
       }
   }

   When used to present an access token as in Section 7, the
   Authorization header MUST be included in the signature.

8.6.  OAuth Proof of Possession (PoP)

   This method is indicated by "oauthpop" in the "proof" field.  The RC
   creates an HTTP Authorization PoP header as described in
   [I-D.ietf-oauth-signed-http-request] section 4, with the following
   additional requirements:

   *  The "at" (access token) field MUST be omitted unless this method
      is being used in conjunction with an access token as in Section 7.
      [[ See issue #112 (https://github.com/ietf-wg-gnap/gnap-core-
      protocol/issues/112) ]]




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   *  The "b" (body hash) field MUST be calculated and supplied, unless
      there is no entity body (such as a GET, OPTIONS, or DELETE
      request).

   *  All components of the URL MUST be calculated and supplied

   *  The m (method) field MUST be supplied

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-Type: application/json
   PoP: eyJhbGciOiJSUzI1NiIsImp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
   QVFBQiIsImtpZCI6Inh5ei1jbGllbnQiLCJhbGciOiJSUzI1NiIsIm4iO
   iJ6d0NUXzNieC1nbGJiSHJoZVlwWXBSV2lZOUktbkVhTVJwWm5ScklqQ3
   M2Yl9lbXlUa0JrRERFalN5c2kzOE9DNzNoajEtV2d4Y1BkS05HWnlJb0g
   zUVplbjFNS3l5aFFwTEpHMS1vTE5McW03cFhYdGRZelNkQzlPMy1vaXl5
   OHlrTzRZVXlOWnJSUmZQY2loZFFDYk9fT0M4UXVnbWc5cmdORE9TcXBwZ
   GFOZWFzMW92OVB4WXZ4cXJ6MS04SGE3Z2tEMDBZRUNYSGFCMDV1TWFVYW
   RIcS1PX1dJdllYaWNnNkk1ajZTNDRWTlU2NVZCd3UtQWx5blR4UWRNQVd
   QM2JZeFZWeTZwMy03ZVRKb2t2allURnFnRFZEWjhsVVhicjV5Q1RuUmhu
   aEpndmYzVmpEX21hbE5lOC10T3FLNU9TRGxIVHk2Z0Q5TnFkR0NtLVBtM
   1EifX0.eyJwIjoiXC9hcGlcL2FzXC90cmFuc2FjdGlvbiIsImIiOiJxa0
   lPYkdOeERhZVBTZnc3NnFjamtqSXNFRmxDb3g5bTU5NFM0M0RkU0xBIiw
   idSI6Imhvc3QuZG9ja2VyLmludGVybmFsIiwiaCI6W1siQWNjZXB0Iiwi
   Q29udGVudC1UeXBlIiwiQ29udGVudC1MZW5ndGgiXSwiVjQ2OUhFWGx6S
   k9kQTZmQU5oMmpKdFhTd3pjSGRqMUloOGk5M0h3bEVHYyJdLCJtIjoiUE
   9TVCIsInRzIjoxNTcyNjQyNjEwfQ.xyQ47qy8bu4fyK1T3Ru1Sway8wp6
   5rfAKnTQQU92AUUU07I2iKoBL2tipBcNCC5zLH5j_WUyjlN15oi_lLHym
   fPdzihtt8_Jibjfjib5J15UlifakjQ0rHX04tPal9PvcjwnyZHFcKn-So
   Y3wsARn-gGwxpzbsPhiKQP70d2eG0CYQMA6rTLslT7GgdQheelhVFW29i
   27NcvqtkJmiAG6Swrq4uUgCY3zRotROkJ13qo86t2DXklV-eES4-2dCxf
   cWFkzBAr6oC4Qp7HnY_5UT6IWkRJt3efwYprWcYouOVjtRan3kEtWkaWr
   G0J4bPVnTI5St9hJYvvh7FE8JirIg

   {
       "resources": [
           "dolphin-metadata"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.foo",
               "nonce": "VJLO6A4CAYLBXHTR0KRO"
           }
       },
       "client": {
         "display": {



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           "name": "My Client Display Name",
           "uri": "https://example.net/client"
         },
         "proof": "oauthpop",
         "key": {
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
   tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
   y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-
   ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
   06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
   bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
   Y1cK2U3obvUg7w"
           }
         }
       }
   }

   [[ See issue #113 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/113) ]]

9.  Discovery

   By design, the protocol minimizes the need for any pre-flight
   discovery.  To begin a request, the RC only needs to know the
   endpoint of the AS and which keys it will use to sign the request.
   Everything else can be negotiated dynamically in the course of the
   protocol.

   However, the AS can have limits on its allowed functionality.  If the
   RC wants to optimize its calls to the AS before making a request, it
   MAY send an HTTP OPTIONS request to the grant request endpoint to
   retrieve the server's discovery information.  The AS MUST respond
   with a JSON document containing the following information:

   grant_request_endpoint (string)  REQUIRED.  The full URL of the AS's
      grant request endpoint.  This MUST match the URL the RC used to
      make the discovery request.

   capabilities (array of strings)  OPTIONAL.  A list of the AS's
      capabilities.  The values of this result MAY be used by the RC in
      the capabilities section (Section 2.6) of the request.

   interaction_methods (array of strings)  OPTIONAL.  A list of the AS's



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      interaction methods.  The values of this list correspond to the
      possible fields in the interaction section (Section 2.5) of the
      request.

   key_proofs (array strings)  OPTIONAL.  A list of the AS's supported
      key proofing mechanisms.  The values of this list correspond to
      possible values of the "proof" field of the key section
      (Section 2.3.2) of the request.

   sub_ids (array of strings)  OPTIONAL.  A list of the AS's supported
      identifiers.  The values of this list correspond to possible
      values of the subject identifier section (Section 2.2) of the
      request.

   assertions (array of strings)  OPTIONAL.  A list of the AS's
      supported assertion formats.  The values of this list correspond
      to possible values of the subject assertion section (Section 2.2)
      of the request.

   The information returned from this method is for optimization
   purposes only.  The AS MAY deny any request, or any portion of a
   request, even if it lists a capability as supported.  For example, a
   given RC can be registered with the "mtls" key proofing mechanism,
   but the AS also returns other proofing methods, then the AS will deny
   a request from that RC using a different proofing mechanism.

10.  Resource Servers

   In some deployments, a resource server will need to be able to call
   the AS for a number of functions.

   [[ See issue #114 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/114) ]]

10.1.  Introspecting a Token

   When the RS receives an access token, it can call the introspection
   endpoint at the AS to get token information.  [[ See issue #115
   (https://github.com/ietf-wg-gnap/gnap-core-protocol/issues/115) ]]

   +------+       +------+       +------+
   |  RC  |--(1)->|  RS  |       |  AS  |
   |      |       |      |--(2)->|      |
   |      |       |      |<-(3)--|      |
   |      |       |      |       +------+
   |      |<-(4)--|      |
   +------+       +------+




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   1.  The RC calls the RS with its access token.

   2.  The RS introspects the access token value at the AS.  The RS
       signs the request with its own key (not the RC's key or the
       token's key).

   3.  The AS validates the token value and the RC's request and returns
       the introspection response for the token.

   4.  The RS fulfills the request from the RC.

   The RS signs the request with its own key and sends the access token
   as the body of the request.

   POST /introspect HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
   }

   The AS responds with a data structure describing the token's current
   state and any information the RS would need to validate the token's
   presentation, such as its intended proofing mechanism and key
   material.

   Content-type: application/json

   {
       "active": true,
       "resources": [
           "dolphin-metadata", "some other thing"
       ],
       "client": {
         "key": {
           "proof": "httpsig",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeL...."
           }
         }
       }
   }



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10.2.  Deriving a downstream token

   Some architectures require an RS to act as an RC and request a
   derived access token for a secondary RS.  This internal token is
   issued in the context of the incoming access token.

   +------+       +-------+       +------+       +-------+
   |  RC  |--(1)->|  RS1  |       |  AS  |       |  RS2  |
   |      |       |       |--(2)->|      |       |       |
   |      |       |       |<-(3)--|      |       |       |
   |      |       |       |       +------+       |       |
   |      |       |       |                      |       |
   |      |       |       |-----------(4)------->|       |
   |      |       |       |<----------(5)--------|       |
   |      |<-(6)--|       |                      |       |
   +------+       +-------+                      +-------+

   1.  The RC calls RS1 with an access token.

   2.  RS1 presents that token to the AS to get a derived token for use
       at RS2.  RS1 indicates that it has no ability to interact with
       the RO.  RS1 signs its request with its own key, not the token's
       key or the RC's key.

   3.  The AS returns a derived token to RS1 for use at RS2.

   4.  RS1 calls RS2 with the token from (3).

   5.  RS2 fulfills the call from RS1.

   6.  RS1 fulfills the call from RC.

   If the RS needs to derive a token from one presented to it, it can
   request one from the AS by making a token request as described in
   Section 2 and presenting the existing access token's value in the
   "existing_access_token" field.

   The RS MUST identify itself with its own key and sign the request.

   [[ See issue #116 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/116) ]]










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 POST /tx HTTP/1.1
 Host: server.example.com
 Content-type: application/json
 Detached-JWS: ejy0...

 {
     "resources": [
         {
             "actions": [
                 "read",
                 "write",
                 "dolphin"
             ],
             "locations": [
                 "https://server.example.net/",
                 "https://resource.local/other"
             ],
             "datatypes": [
                 "metadata",
                 "images"
             ]
         },
         "dolphin-metadata"
     ],
     "client": "7C7C4AZ9KHRS6X63AJAO",
     "existing_access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0"
 }

   The AS responds with a token as described in Section 3.

10.3.  Registering a Resource Handle

   If the RS needs to, it can post a set of resources as described in
   Section 2.1.1 to the AS's resource registration endpoint.

   The RS MUST identify itself with its own key and sign the request.















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   POST /resource HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata"
       ],
       "client": "7C7C4AZ9KHRS6X63AJAO"

   }

   The AS responds with a handle appropriate to represent the resources
   list that the RS presented.

   Content-type: application/json

   {
       "resource_handle": "FWWIKYBQ6U56NL1"
   }

   The RS MAY make this handle available as part of a response
   (Section 10.4) or as documentation to developers.

   [[ See issue #117 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/117) ]]









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10.4.  Requesting Resources With Insufficient Access

   If the RC calls an RS without an access token, or with an invalid
   access token, the RS MAY respond to the RC with an authentication
   header indicating that GNAP needs to be used to access the resource.
   The address of the GNAP endpoint MUST be sent in the "as_uri"
   parameter.  The RS MAY additionally return a resource reference that
   the RC MAY use in its resource request (Section 2.1).  This resource
   reference handle SHOULD be sufficient for at least the action the RC
   was attempting to take at the RS.  The RS MAY use the dynamic
   resource handle request (Section 10.3) to register a new resource
   handle, or use a handle that has been pre-configured to represent
   what the AS is protecting.  The content of this handle is opaque to
   the RS and the RC.

WWW-Authenticate: GNAP as_uri=http://server.example/tx,resource=FWWIKYBQ6U56NL1

   The RC then makes a call to the "as_uri" as described in Section 2,
   with the value of "resource" as one of the members of a "resources"
   array Section 2.1.1.  The RC MAY request additional resources and
   other information, and MAY request multiple access tokens.

   [[ See issue #118 (https://github.com/ietf-wg-gnap/gnap-core-
   protocol/issues/118) ]]

11.  Acknowledgements

   The author would like to thank the feedback of the following
   individuals for their reviews, implementations, and contributions:
   Aaron Parecki, Annabelle Backman, Dick Hardt, Dmitri Zagidulin,
   Dmitry Barinov, Fabien Imbault, Francis Pouatcha, George Fletcher,
   Haardik Haardik, Hamid Massaoud, Jacky Yuan, Joseph Heenan, Kathleen
   Moriarty, Mike Jones, Mike Varley, Nat Sakimura, Takahiko Kawasaki,
   Takahiro Tsuchiya.

   In particular, the author would like to thank Aaron Parecki and Mike
   Jones for insights into how to integrate identity and authentication
   systems into the core protocol, and to Dick Hardt for the use cases,
   diagrams, and insights provided in the XAuth proposal that have been
   incorporated here.  The author would like to especially thank Mike
   Varley and the team at SecureKey for feedback and development of
   early versions of the XYZ protocol that fed into this standards work.

12.  IANA Considerations

   [[ TBD: There are a lot of items in the document that are expandable
   through the use of value registries. ]]




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13.  Security Considerations

   [[ TBD: There are a lot of security considerations to add. ]]

   All requests have to be over TLS or equivalent as per [BCP195].  Many
   handles act as shared secrets, though they can be combined with a
   requirement to provide proof of a key as well.

14.  Privacy Considerations

   [[ TBD: There are a lot of privacy considerations to add. ]]

   Handles are passed between parties and therefore should not contain
   any private data.

   When user information is passed to the RC, the AS needs to make sure
   that it has the permission to do so.

15.  Normative References

   [BCP195]   Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", May 2015,
              <http://www.rfc-editor.org/info/bcp195>.

   [I-D.ietf-httpbis-message-signatures]
              Backman, A., Richer, J., and M. Sporny, "Signing HTTP
              Messages", Work in Progress, Internet-Draft, draft-ietf-
              httpbis-message-signatures-00, 10 April 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-httpbis-
              message-signatures-00.txt>.

   [I-D.ietf-oauth-dpop]
              Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
              Jones, M., and D. Waite, "OAuth 2.0 Demonstration of
              Proof-of-Possession at the Application Layer (DPoP)", Work
              in Progress, Internet-Draft, draft-ietf-oauth-dpop-01, 1
              May 2020, <http://www.ietf.org/internet-drafts/draft-ietf-
              oauth-dpop-01.txt>.

   [I-D.ietf-oauth-signed-http-request]
              Richer, J., Bradley, J., and H. Tschofenig, "A Method for
              Signing HTTP Requests for OAuth", Work in Progress,
              Internet-Draft, draft-ietf-oauth-signed-http-request-03, 8
              August 2016, <http://www.ietf.org/internet-drafts/draft-
              ietf-oauth-signed-http-request-03.txt>.




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   [I-D.ietf-secevent-subject-identifiers]
              Backman, A. and M. Scurtescu, "Subject Identifiers for
              Security Event Tokens", Work in Progress, Internet-Draft,
              draft-ietf-secevent-subject-identifiers-06, 4 September
              2020, <http://www.ietf.org/internet-drafts/draft-ietf-
              secevent-subject-identifiers-06.txt>.

   [OIDC]     Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0 incorporating
              errata set 1", November 2014,
              <https://openiD.net/specs/openiD-connect-core-1_0.html>.

   [OIDC4IA]  Lodderstedt, T. and D. Fett, "OpenID Connect for Identity
              Assurance 1.0", October 2019, <https://openid.net/specs/
              openid-connect-4-identity-assurance-1_0.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3230]  Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
              RFC 3230, DOI 10.17487/RFC3230, January 2002,
              <https://www.rfc-editor.org/info/rfc3230>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <https://www.rfc-editor.org/info/rfc5646>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7797]  Jones, M., "JSON Web Signature (JWS) Unencoded Payload
              Option", RFC 7797, DOI 10.17487/RFC7797, February 2016,
              <https://www.rfc-editor.org/info/rfc7797>.






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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8693]  Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J.,
              and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693,
              DOI 10.17487/RFC8693, January 2020,
              <https://www.rfc-editor.org/info/rfc8693>.

   [RFC8705]  Campbell, B., Bradley, J., Sakimura, N., and T.
              Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
              and Certificate-Bound Access Tokens", RFC 8705,
              DOI 10.17487/RFC8705, February 2020,
              <https://www.rfc-editor.org/info/rfc8705>.

Appendix A.  Document History

   *  -02

      -  Moved all "editor's note" items to GitHub Issues.

   *  -01

      -  "updated_at" subject info timestamp now in ISO 8601 string
         format.

      -  Editorial fixes.

      -  Added Aaron and Fabien as document authors.

   *  -00

      -  Initial working group draft.

Appendix B.  Component Data Models

   While different implementations of this protocol will have different
   realizations of all the components and artifacts enumerated here, the
   nature of the protocol implies some common structures and elements
   for certain components.  This appendix seeks to enumerate those
   common elements.





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   TBD: Client has keys, allowed requested resources, identifier(s),
   allowed requested subjects, allowed

   TBD: AS has "grant endpoint", interaction endpoints, store of trusted
   client keys, policies

   TBD: Token has RO, user, client, resource list, RS list,

Appendix C.  Example Protocol Flows

   The protocol defined in this specification provides a number of
   features that can be combined to solve many different kinds of
   authentication scenarios.  This section seeks to show examples of how
   the protocol would be applied for different situations.

   Some longer fields, particularly cryptographic information, have been
   truncated for display purposes in these examples.

C.1.  Redirect-Based User Interaction

   In this scenario, the user is the RO and has access to a web browser,
   and the client can take front-channel callbacks on the same device as
   the user.  This combination is analogous to the OAuth 2 Authorization
   Code grant type.

   The client initiates the request to the AS.  Here the client
   identifies itself using its public key.
























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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           }
       ],
       "client": {
         "key": {
           "proof": "jwsd",
           "jwk": {
               "kty": "RSA",
               "e": "AQAB",
               "kid": "xyz-1",
               "alg": "RS256",
               "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
           }
         }
       },
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }
   }







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   The AS processes the request and determines that the RO needs to
   interact.  The AS returns the following response giving the client
   the information it needs to connect.  The AS has also indicated to
   the client that it can use the given instance identifier to identify
   itself in future requests (Section 2.3.1).

Content-type: application/json

{
    "interact": {
       "redirect": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
       "callback": "MBDOFXG4Y5CVJCX821LH"
    }
    "continue": {
        "access_token": {
            "value": "80UPRY5NM33OMUKMKSKU",
            "key": true
        },
        "uri": "https://server.example.com/continue"
    },
    "instance_id": "7C7C4AZ9KHRS6X63AJAO"
}

   The client saves the response and redirects the user to the
   interaction_url by sending the following HTTP message to the user's
   browser.

   HTTP 302 Found
   Location: https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ

   The user's browser fetches the AS's interaction URL.  The user logs
   in, is identified as the RO for the resource being requested, and
   approves the request.  Since the AS has a callback parameter, the AS
   generates the interaction reference, calculates the hash, and
   redirects the user back to the client with these additional values
   added as query parameters.

HTTP 302 Found
Location: https://client.example.net/return/123455
  ?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
  &interact_ref=4IFWWIKYBC2PQ6U56NL1










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   The client receives this request from the user's browser.  The client
   ensures that this is the same user that was sent out by validating
   session information and retrieves the stored pending request.  The
   client uses the values in this to validate the hash parameter.  The
   client then calls the continuation URL and presents the handle and
   interaction reference in the request body.  The client signs the
   request as above.

   POST /continue HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   {
       "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

   The AS retrieves the pending request based on the handle and issues a
   bearer access token and returns this to the client.































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Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [{
            "actions": [
                "read",
                "write",
                "dolphin"
            ],
            "locations": [
                "https://server.example.net/",
                "https://resource.local/other"
            ],
            "datatypes": [
                "metadata",
                "images"
            ]
        }]
    },
    "continue": {
        "access_token": {
            "value": "80UPRY5NM33OMUKMKSKU",
            "key": true
        },
        "uri": "https://server.example.com/continue"
    }
}

C.2.  Secondary Device Interaction

   In this scenario, the user does not have access to a web browser on
   the device and must use a secondary device to interact with the AS.
   The client can display a user code or a printable QR code.  The
   client prefers a short URL if one is available, with a maximum of 255
   characters in length.  The is not able to accept callbacks from the
   AS and needs to poll for updates while waiting for the user to
   authorize the request.

   The client initiates the request to the AS.








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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "dolphin-metadata", "some other thing"
       ],
       "client": "7C7C4AZ9KHRS6X63AJAO",
       "interact": {
           "redirect": 255,
           "user_code": true
       }
   }

   The AS processes this and determines that the RO needs to interact.
   The AS supports both long and short redirect URIs for interaction, so
   it includes both.  Since there is no "callback" the AS does not
   include a nonce, but does include a "wait" parameter on the
   continuation section because it expects the client to poll for
   results.

Content-type: application/json

{
    "interact": {
        "redirect": "https://srv.ex/MXKHQ",
        "user_code": {
            "code": "A1BC-3DFF",
            "url": "https://srv.ex/device"
        }
    },
    "continue": {
        "uri": "https://server.example.com/continue/80UPRY5NM33OMUKMKSKU",
        "wait": 60
    }
}

   The client saves the response and displays the user code visually on
   its screen along with the static device URL.  The client also
   displays the short interaction URL as a QR code to be scanned.

   If the user scans the code, they are taken to the interaction
   endpoint and the AS looks up the current pending request based on the
   incoming URL.  If the user instead goes to the static page and enters
   the code manually, the AS looks up the current pending request based
   on the value of the user code.  In both cases, the user logs in, is



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   identified as the RO for the resource being requested, and approves
   the request.  Once the request has been approved, the AS displays to
   the user a message to return to their device.

   Meanwhile, the client periodically polls the AS every 60 seconds at
   the continuation URL.  The client signs the request using the same
   key and method that it did in the first request.

   POST /continue/80UPRY5NM33OMUKMKSKU HTTP/1.1
   Host: server.example.com
   Detached-JWS: ejy0...

   The AS retrieves the pending request based on the handle and
   determines that it has not yet been authorized.  The AS indicates to
   the client that no access token has yet been issued but it can
   continue to call after another 60 second timeout.

Content-type: application/json

{
    "continue": {
        "uri": "https://server.example.com/continue/BI9QNW6V9W3XFJK4R02D",
        "wait": 60
    }
}

   Note that the continuation URL has been rotated since it was used by
   the client to make this call.  The client polls the continuation URL
   after a 60 second timeout using the new handle.

   POST /continue/BI9QNW6V9W3XFJK4R02D HTTP/1.1
   Host: server.example.com
   Authorization: GNAP
   Detached-JWS: ejy0...

   The AS retrieves the pending request based on the URL, determines
   that it has been approved, and issues an access token.














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Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "dolphin-metadata", "some other thing"
        ]
    }
}

Appendix D.  No User Involvement

   In this scenario, the client is requesting access on its own behalf,
   with no user to interact with.

   The client creates a request to the AS, identifying itself with its
   public key and using MTLS to make the request.

   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json

   {
       "resources": [
           "backend service", "nightly-routine-3"
       ],
       "client": {
         "key": {
           "proof": "mtls",
           "cert#S256": "bwcK0esc3ACC3DB2Y5_lESsXE8o9ltc05O89jdN-dg2"
         }
       }
   }

   The AS processes this and determines that the client can ask for the
   requested resources and issues an access token.












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   Content-type: application/json

   {
       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "key": true,
           "manage": "https://server.example.com/token",
           "resources": [
               "backend service", "nightly-routine-3"
           ]
       }
   }

D.1.  Asynchronous Authorization

   In this scenario, the client is requesting on behalf of a specific
   RO, but has no way to interact with the user.  The AS can
   asynchronously reach out to the RO for approval in this scenario.

   The client starts the request at the AS by requesting a set of
   resources.  The client also identifies a particular user.






























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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           {
               "type": "photo-api",
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "read", "dolphin-metadata",
           {
               "type": "financial-transaction",
               "actions": [
                   "withdraw"
               ],
               "identifier": "account-14-32-32-3",
               "currency": "USD"
           },
           "some other thing"
       ],
       "client": "7C7C4AZ9KHRS6X63AJAO",
       "user": {
           "sub_ids": [ {
               "subject_type": "email",
               "email": "user@example.com"
           } ]
      }
   }

   The AS processes this and determines that the RO needs to interact.
   The AS determines that it can reach the identified user
   asynchronously and that the identified user does have the ability to
   approve this request.  The AS indicates to the client that it can
   poll for continuation.



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   Content-type: application/json

   {
       "continue": {
           "access_token": {
               "value": "80UPRY5NM33OMUKMKSKU",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   The AS reaches out to the RO and prompts them for consent.  In this
   example, the AS has an application that it can push notifications in
   to for the specified account.

   Meanwhile, the client periodically polls the AS every 60 seconds at
   the continuation URL.

   POST /continue HTTP/1.1
   Host: server.example.com
   Authorization: GNAP 80UPRY5NM33OMUKMKSKU
   Detached-JWS: ejy0...

   The AS retrieves the pending request based on the handle and
   determines that it has not yet been authorized.  The AS indicates to
   the client that no access token has yet been issued but it can
   continue to call after another 60 second timeout.

   Content-type: application/json

   {
       "continue": {
           "access_token": {
               "value": "BI9QNW6V9W3XFJK4R02D",
               "key": true
           },
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   Note that the continuation handle has been rotated since it was used
   by the client to make this call.  The client polls the continuation
   URL after a 60 second timeout using the new handle.





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   POST /continue HTTP/1.1
   Host: server.example.com
   Authorization: GNAP BI9QNW6V9W3XFJK4R02D
   Detached-JWS: ejy0...

   The AS retrieves the pending request based on the handle and
   determines that it has been approved and it issues an access token.

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "key": false,
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "dolphin-metadata", "some other thing"
        ]
    }
}

D.2.  Applying OAuth 2 Scopes and Client IDs

   While GNAP is not designed to be directly compatible with OAuth 2
   [RFC6749], considerations have been made to enable the use of OAuth 2
   concepts and constructs more smoothly within GNAP.

   In this scenario, the client developer has a "client_id" and set of
   "scope" values from their OAuth 2 system and wants to apply them to
   the new protocol.  Traditionally, the OAuth 2 client developer would
   put their "client_id" and "scope" values as parameters into a
   redirect request to the authorization endpoint.

   HTTP 302 Found
   Location: https://server.example.com/authorize
     ?client_id=7C7C4AZ9KHRS6X63AJAO
     &scope=read%20write%20dolphin
     &redirect_uri=https://client.example.net/return
     &response_type=code
     &state=123455

   Now the developer wants to make an analogous request to the AS using
   the new protocol.  To do so, the client makes an HTTP POST and places
   the OAuth 2 values in the appropriate places.







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   POST /tx HTTP/1.1
   Host: server.example.com
   Content-type: application/json
   Detached-JWS: ejy0...

   {
       "resources": [
           "read", "write", "dolphin"
       ],
       "client": "7C7C4AZ9KHRS6X63AJAO",
       "interact": {
           "redirect": true,
           "callback": {
               "method": "redirect",
               "uri": "https://client.example.net/return?state=123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       }
   }

   The client_id can be used to identify the client's keys that it uses
   for authentication, the scopes represent resources that the client is
   requesting, and the "redirect_uri" and "state" value are pre-combined
   into a "callback" URI that can be unique per request.  The client
   additionally creates a nonce to protect the callback, separate from
   the state parameter that it has added to its return URL.

   From here, the protocol continues as above.

Appendix E.  JSON Structures and Polymorphism

   GNAP makes use of polymorphism within the JSON [RFC8259] structures
   used for the protocol.  Each portion of this protocol is defined in
   terms of the JSON data type that its values can take, whether it's a
   string, object, array, boolean, or number.  For some fields,
   different data types offer different descriptive capabilities and are
   used in different situations for the same field.  Each data type
   provides a different syntax to express the same underlying semantic
   protocol element, which allows for optimization and simplification in
   many common cases.

   Even though JSON is often used to describe strongly typed structures,
   JSON on its own is naturally polymorphic.  In JSON, the named members
   of an object have no type associated with them, and any data type can
   be used as the value for any member.  In practice, each member has a
   semantic type that needs to make sense to the parties creating and
   consuming the object.  Within this protocol, each object member is
   defined in terms of its semantic content, and this semantic content



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   might have expressions in different concrete data types for different
   specific purposes.  Since each object member has exactly one value in
   JSON, each data type for an object member field is naturally mutually
   exclusive with other data types within a single JSON object.

   For example, a resource request for a single access token is composed
   of an array of resource request descriptions while a request for
   multiple access tokens is composed of an object whose member values
   are all arrays.  Both of these represent requests for access, but the
   difference in syntax allows the RC and AS to differentiate between
   the two request types in the same request.

   Another form of polymorphism in JSON comes from the fact that the
   values within JSON arrays need not all be of the same JSON data type.
   However, within this protocol, each element within the array needs to
   be of the same kind of semantic element for the collection to make
   sense, even when the data types are different from each other.

   For example, each aspect of a resource request can be described using
   an object with multiple dimensional components, or the aspect can be
   requested using a string.  In both cases, the resource request is
   being described in a way that the AS needs to interpret, but with
   different levels of specificity and complexity for the RC to deal
   with.  An API designer can provide a set of common access scopes as
   simple strings but still allow RC developers to specify custom access
   when needed for more complex APIs.

   Extensions to this specification can use different data types for
   defined fields, but each extension needs to not only declare what the
   data type means, but also provide justification for the data type
   representing the same basic kind of thing it extends.  For example,
   an extension declaring an "array" representation for a field would
   need to explain how the array represents something akin to the non-
   array element that it is replacing.

Authors' Addresses

   Justin Richer (editor)
   Bespoke Engineering

   Email: ietf@justin.richer.org
   URI:   https://bspk.io/


   Aaron Parecki
   Okta

   Email: aaron@parecki.com



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   URI:   https://aaronparecki.com


   Fabien Imbault
   acert.io

   Email: fabien.imbault@acert.io
   URI:   https://acert.io/











































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