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Versions: (draft-jones-oauth-token-exchange) 00 01 02 03 04 05 06 07 08 09 10

OAuth Working Group                                             M. Jones
Internet-Draft                                                A. Nadalin
Intended status: Standards Track                               Microsoft
Expires: June 3, 2018                                   B. Campbell, Ed.
                                                              J. Bradley
                                                           Ping Identity
                                                            C. Mortimore
                                                              Salesforce
                                                       November 30, 2017


                        OAuth 2.0 Token Exchange
                   draft-ietf-oauth-token-exchange-10

Abstract

   This specification defines a protocol for an HTTP- and JSON- based
   Security Token Service (STS) by defining how to request and obtain
   security tokens from OAuth 2.0 authorization servers, including
   security tokens employing impersonation and delegation.

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 June 3, 2018.

Copyright Notice

   Copyright (c) 2017 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Delegation vs. Impersonation Semantics  . . . . . . . . .   4
     1.2.  Requirements Notation and Conventions . . . . . . . . . .   5
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Token Exchange Request and Response . . . . . . . . . . . . .   6
     2.1.  Request . . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.1.  Relationship Between Resource, Audience and Scope . .   8
     2.2.  Response  . . . . . . . . . . . . . . . . . . . . . . . .   8
       2.2.1.  Successful Response . . . . . . . . . . . . . . . . .   8
       2.2.2.  Error Response  . . . . . . . . . . . . . . . . . . .  10
     2.3.  Example Token Exchange  . . . . . . . . . . . . . . . . .  10
   3.  Token Type Identifiers  . . . . . . . . . . . . . . . . . . .  12
   4.  JSON Web Token Claims and Introspection Response Parameters .  13
     4.1.  "act" (Actor) Claim . . . . . . . . . . . . . . . . . . .  13
     4.2.  "scp" (Scopes) Claim  . . . . . . . . . . . . . . . . . .  15
     4.3.  "cid" (Client Identifier) Claim . . . . . . . . . . . . .  16
     4.4.  "may_act" (May Act For) Claim . . . . . . . . . . . . . .  16
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     5.1.  OAuth URI Registration  . . . . . . . . . . . . . . . . .  17
       5.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .  17
     5.2.  OAuth Parameters Registration . . . . . . . . . . . . . .  18
       5.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  18
     5.3.  OAuth Access Token Type Registration  . . . . . . . . . .  19
       5.3.1.  Registry Contents . . . . . . . . . . . . . . . . . .  19
     5.4.  JSON Web Token Claims Registration  . . . . . . . . . . .  19
       5.4.1.  Registry Contents . . . . . . . . . . . . . . . . . .  20
     5.5.  OAuth Token Introspection Response Registration . . . . .  20
       5.5.1.  Registry Contents . . . . . . . . . . . . . . . . . .  20
     5.6.  OAuth Extensions Error Registration . . . . . . . . . . .  20
       5.6.1.  Registry Contents . . . . . . . . . . . . . . . . . .  21
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Appendix A.  Additional Token Exchange Examples . . . . . . . . .  23
     A.1.  Impersonation Token Exchange Example  . . . . . . . . . .  23
       A.1.1.  Token Exchange Request  . . . . . . . . . . . . . . .  23
       A.1.2.  Subject Token Claims  . . . . . . . . . . . . . . . .  24
       A.1.3.  Token Exchange Response . . . . . . . . . . . . . . .  24
       A.1.4.  Issued Token Claims . . . . . . . . . . . . . . . . .  25



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     A.2.  Delegation Token Exchange Example . . . . . . . . . . . .  25
       A.2.1.  Token Exchange Request  . . . . . . . . . . . . . . .  25
       A.2.2.  Subject Token Claims  . . . . . . . . . . . . . . . .  26
       A.2.3.  Actor Token Claims  . . . . . . . . . . . . . . . . .  27
       A.2.4.  Token Exchange Response . . . . . . . . . . . . . . .  27
       A.2.5.  Issued Token Claims . . . . . . . . . . . . . . . . .  27
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  28
   Appendix C.  Document History . . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   A security token is a set of information that facilitates the sharing
   of identity and security information in heterogeneous environments or
   across security domains.  Examples of security tokens include JSON
   Web Tokens (JWTs) [JWT] and SAML 2.0 Assertions
   [OASIS.saml-core-2.0-os].  Security tokens are typically signed to
   achieve integrity and sometimes also encrypted to achieve
   confidentiality.  Security tokens are also sometimes described as
   Assertions, such as in [RFC7521].

   A Security Token Service (STS) is a service capable of validating and
   issuing security tokens, which enables clients to obtain appropriate
   access credentials for resources in heterogeneous environments or
   across security domains.  Web Service clients have used WS-Trust
   [WS-Trust] as the protocol to interact with an STS for token
   exchange.  While WS-Trust uses XML and SOAP, the trend in modern Web
   development has been towards RESTful patterns and JSON.  The OAuth
   2.0 Authorization Framework [RFC6749] and OAuth 2.0 Bearer Tokens
   [RFC6750] have emerged as popular standards for authorizing and
   securing access to HTTP and RESTful resources but do not provide
   everything necessary to facilitate token exchange interactions.

   This specification defines a protocol extending OAuth 2.0 that
   enables clients to request and obtain security tokens from
   authorization servers acting in the role of an STS.  Similar to OAuth
   2.0, this specification focuses on client developer simplicity and
   requires only an HTTP client and JSON parser, which are nearly
   universally available in modern development environments.  The STS
   protocol defined in this specification is not itself RESTful (an STS
   doesn't lend itself particularly well to a REST approach) but does
   utilize communication patterns and data formats that should be
   familiar to developers accustomed to working with RESTful systems.

   A new grant type for a token exchange request and the associated
   specific parameters for such a request to the token endpoint are
   defined by this specification.  A token exchange response is a normal




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   OAuth 2.0 response from the token endpoint with a few additional
   parameters defined herein to provide information to the client.

   The entity that makes the request to exchange tokens is considered
   the client in the context of the token exchange interaction.
   However, that does not restrict usage of this profile to traditional
   OAuth clients.  An OAuth resource server, for example, might assume
   the role of the client during token exchange in order to trade an
   access token, which it received in a protected resource request, for
   a new token that is appropriate to include in a call to a backend
   service.  The new token might be an access token that is more
   narrowly scoped for the downstream service or it could be an entirely
   different kind of token.

   The scope of this specification is limited to the definition of a
   basic request and response protocol for an STS-style token exchange
   utilizing OAuth 2.0.  Although a few new JWT claims are defined that
   enable delegation semantics to be expressed, the specific syntax,
   semantics and security characteristics of the tokens themselves (both
   those presented to the AS and those obtained by the client) are
   explicitly out of scope and no requirements are placed on the trust
   model in which an implementation might be deployed.  Additional
   profiles may provide more detailed requirements around the specific
   nature of the parties and trust involved, such as whether signing
   and/or encryption of tokens is needed or if proof-of-possession style
   tokens will be required or issued; however, such details will often
   be policy decisions made with respect to the specific needs of
   individual deployments and will be configured or implemented
   accordingly.

   The security tokens obtained may be used in a number of contexts, the
   specifics of which are also beyond the scope of this specification.

1.1.  Delegation vs. Impersonation Semantics

   When principal A impersonates principal B, A is given all the rights
   that B has within some defined rights context and is
   indistinguishable from B in that context.  Thus, when principal A
   impersonates principal B, then in so far as any entity receiving such
   a token is concerned, they are actually dealing with B.  It is true
   that some members of the identity system might have awareness that
   impersonation is going on, but it is not a requirement.  For all
   intents and purposes, when A is impersonating B, A is B.

   Delegation semantics are different than impersonation semantics,
   though the two are closely related.  With delegation semantics,
   principal A still has its own identity separate from B and it is
   explicitly understood that while B may have delegated some of its



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   rights to A, any actions taken are being taken by A representing B.
   In a sense, A is an agent for B.

   Delegation and impersonation are not inclusive of all situations.
   When a principal is acting directly on its own behalf, for example,
   neither delegation nor impersonation are in play.  They are, however,
   the more common semantics operating for token exchange and, as such,
   are given more direct treatment in this specification.

   Delegation semantics are typically expressed in a token by including
   information about both the primary subject of the token as well as
   the actor to whom that subject has delegated some of its rights.
   Such a token is sometimes referred to as a composite token because it
   is composed of information about multiple subjects.  Typically, in
   the request, the "subject_token" represents the identity of the party
   on behalf of whom the token is being requested while the
   "actor_token" represents the identity of the party to whom the access
   rights of the issued token are being delegated.  A composite token
   issued by the authorization server will contain information about
   both parties.  When and if a composite token is issued is at the
   discretion of the authorization server and applicable policy and
   configuration.

   The specifics of representing a composite token and even whether or
   not such a token will be issued depend on the details of the
   implementation and the kind of token.  The representations of
   composite tokens that are not JWTs are beyond the scope of this
   specification.  The "actor_token" request parameter, however, does
   provide a means for providing information about the desired actor and
   the JWT "act" claim can provide a representation of a chain of
   delegation.

1.2.  Requirements Notation and Conventions

   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 RFC
   2119 [RFC2119].

1.3.  Terminology

   This specification uses the terms "access token type", "authorization
   server", "client", "client identifier", "resource server", "token
   endpoint", "token request", and "token response" defined by OAuth 2.0
   [RFC6749], and the terms "Base64url Encoding", "Claim", and "JWT
   Claims Set" defined by JSON Web Token (JWT) [JWT].





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2.  Token Exchange Request and Response

2.1.  Request

   A client requests a security token by making a token request to the
   authorization server's token endpoint using the extension grant type
   mechanism defined in Section 4.5 of OAuth 2.0 [RFC6749].

   Client authentication to the authorization server is done using the
   normal mechanisms provided by OAuth 2.0.  Section 2.3.1 of The OAuth
   2.0 Authorization Framework [RFC6749] defines password-based
   authentication of the client, however, client authentication is
   extensible and other mechanisms are possible.  For example, [RFC7523]
   defines client authentication using JSON Web Tokens (JWTs) [JWT].
   The supported methods of client authentication and whether or not to
   allow unauthenticated or unidentified clients are deployment
   decisions that are at the discretion of the authorization server.

   The client makes a token exchange request to the token endpoint with
   an extension grant type by including the following parameters using
   the "application/x-www-form-urlencoded" format with a character
   encoding of UTF-8 in the HTTP request entity-body:

   grant_type
      REQUIRED.  The value "urn:ietf:params:oauth:grant-type:token-
      exchange" indicates that a token exchange is being performed.

   resource
      OPTIONAL.  Indicates the physical location of the target service
      or resource where the client intends to use the requested security
      token.  This enables the authorization server to apply policy as
      appropriate for the target, such as determining the type and
      content of the token to be issued or if and how the token is to be
      encrypted.  In many cases, a client will not have knowledge of the
      logical organization of the systems with which it interacts and
      will only know the location of the service where it intends to use
      the token.  The "resource" parameter allows the client to indicate
      to the authorization server where it intends to use the issued
      token by providing the location, typically as an https URL, in the
      token exchange request in the same form that will be used to
      access that resource.  The authorization server will typically
      have the capability to map from a resource URI value to an
      appropriate policy.  The value of the "resource" parameter MUST be
      an absolute URI, as specified by Section 4.3 of [RFC3986], which
      MAY include a query component and MUST NOT include a fragment
      component.  Multiple "resource" parameters may be used to indicate
      that the issued token is intended to be used at the multiple
      resources listed.



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   audience
      OPTIONAL.  The logical name of the target service where the client
      intends to use the requested security token.  This serves a
      purpose similar to the "resource" parameter, but with the client
      providing a logical name rather than a physical location.
      Interpretation of the name requires that the value be something
      that both the client and the authorization server understand.  An
      OAuth client identifier, a SAML entity identifier
      [OASIS.saml-core-2.0-os], an OpenID Connect Issuer Identifier
      [OpenID.Core], or a URI are examples of things that might be used
      as "audience" parameter values.  Multiple "audience" parameters
      may be used to indicate that the issued token is intended to be
      used at the multiple audiences listed.  The "audience" and
      "resource" parameters may be used together to indicate multiple
      target services with a mix of logical names and physical
      locations.

   scope
      OPTIONAL.  A list of space-delimited, case-sensitive strings that
      allow the client to specify the desired scope of the requested
      security token in the context of the service or resource where the
      token will be used.

   requested_token_type
      OPTIONAL.  An identifier, as described in Section 3, for the type
      of the requested security token.  If the requested type is
      unspecified, the issued token type is at the discretion of the
      authorization server and may be dictated by knowledge of the
      requirements of the service or resource indicated by the
      "resource" or "audience" parameter.

   subject_token
      REQUIRED.  A security token that represents the identity of the
      party on behalf of whom the request is being made.  Typically, the
      subject of this token will be the subject of the security token
      issued in response to this request.

   subject_token_type
      REQUIRED.  An identifier, as described in Section 3, that
      indicates the type of the security token in the "subject_token"
      parameter.

   actor_token
      OPTIONAL.  A security token that represents the identity of the
      acting party.  Typically, this will be the party that is
      authorized to use the requested security token and act on behalf
      of the subject.




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   actor_token_type
      An identifier, as described in Section 3, that indicates the type
      of the security token in the "actor_token" parameter.  This is
      REQUIRED when the "actor_token" parameter is present in the
      request but MUST NOT be included otherwise.

   In the absence of one-time-use or other semantics specific to the
   token type, the act of performing a token exchange has no impact on
   the validity of the subject token or actor token.  Furthermore, the
   validity of the subject token or actor token have no impact on the
   validity of the issued token after the exchange has occurred.

2.1.1.  Relationship Between Resource, Audience and Scope

   When requesting a token, the client can indicate the desired target
   service(s) where it intends to use that token by way of the
   "audience" and "resource" parameters, as well as indicating the
   desired scope of the requested token using the "scope" parameter.
   The semantics of such a request are that the client is asking for a
   token with the requested scope that is usable at all the requested
   target services.  Effectively, the requested access rights of the
   token are the cartesian product of all the scopes at all the target
   services.

   An authorization server may be unwilling or unable to fulfill any
   token request but the likelihood of an unfulfillable request is
   significantly higher when very broad access rights are being
   solicited.  As such, in the absence of specific knowledge about the
   relationship of systems in a deployment, clients should exercise
   discretion in the breadth of the access requested, particularly the
   number of target services.  An authorization server can use the
   "invalid_target" error code, defined in Section 2.2.2, to inform a
   client that it requested access to too many target services
   simultaneously.

2.2.  Response

   The authorization server responds to a token exchange request with a
   normal OAuth 2.0 response from the token endpoint, as specified in
   Section 5 of [RFC6749].  Additional details and explanation are
   provided in the following subsections.

2.2.1.  Successful Response

   If the request is valid and meets all policy and other criteria of
   the authorization server, a successful token response is constructed
   by adding the following parameters to the entity-body of the HTTP
   response using the "application/json" media type, as specified by



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   [RFC7159], and an HTTP 200 status code.  The parameters are
   serialized into a JavaScript Object Notation (JSON) structure by
   adding each parameter at the top level.  Parameter names and string
   values are included as JSON strings.  Numerical values are included
   as JSON numbers.  The order of parameters does not matter and can
   vary.

   access_token
      REQUIRED.  The security token issued by the authorization server
      in response to the token exchange request.  The "access_token"
      parameter from Section 5.1 of [RFC6749] is used here to carry the
      requested token, which allows this token exchange protocol to use
      the existing OAuth 2.0 request and response constructs defined for
      the token endpoint.  The identifier "access_token" is used for
      historical reasons and the issued token need not be an OAuth
      access token.

   issued_token_type
      REQUIRED.  An identifier, as described in Section 3, for the
      representation of the issued security token.

   token_type
      REQUIRED.  A case-insensitive value specifying the method of using
      the access token issued, as specified in Section 7.1 of [RFC6749].
      It provides the client with information about how to utilize the
      access token to access protected resources.  For example, a value
      of "Bearer", as specified in [RFC6750], indicates that the
      security token is a bearer token and the client can simply present
      it as is without any additional proof of eligibility beyond the
      contents of the token itself.  Note that the meaning of this
      parameter is different from the meaning of the "issued_token_type"
      parameter, which declares the representation of the issued
      security token; the term "token type" is typically used with this
      meaning, as it is in all "*_token_type" parameters in this
      specification.  If the issued token is not an access token or
      usable as an access token, then the "token_type" value "N_A" is
      used to indicate that an OAuth 2.0 "token_type" identifier is not
      applicable in that context.

   expires_in
      RECOMMENDED.  The validity lifetime, in seconds, of the token
      issued by the authorization server.  Oftentimes the client will
      not have the inclination or capability to inspect the content of
      the token and this parameter provides a consistent and token type
      agnostic indication of how long the token can be expected to be
      valid.  For example, the value 1800 denotes that the token will
      expire in thirty minutes from the time the response was generated.




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   scope
      OPTIONAL, if the scope of the issued security token is identical
      to the scope requested by the client; otherwise, REQUIRED.

   refresh_token
      OPTIONAL.  A refresh token will typically not be issued when the
      exchange is of one temporary credential (the subject_token) for a
      different temporary credential (the issued token) for use in some
      other context.  A refresh token can be issued in cases where the
      client of the token exchange needs the ability to access a
      resource even when the original credential is no longer valid
      (e.g., user-not-present or offline scenarios where there is no
      longer any user entertaining an active session with the client).
      Profiles or deployments of this specification should clearly
      document the conditions under which a client should expect a
      refresh token in response to "urn:ietf:params:oauth:grant-
      type:token-exchange" grant type requests.

2.2.2.  Error Response

   If either the "subject_token" or "actor_token" are invalid for any
   reason, or are unacceptable based on policy, the authorization server
   MUST construct an error response, as specified in Section 5.2 of
   [RFC6749].  The value of the "error" parameter MUST be the
   "invalid_request" error code.

   If the authorization server is unwilling or unable to issue a token
   for all the target services indicated by the "resource" or "audience"
   parameters, the "invalid_target" error code SHOULD be used in the
   error response.

   The authorization server MAY include additional information regarding
   the reasons for the error using the "error_description" and/or
   "error_uri" parameters.

   Other error codes may also be used, as appropriate.

2.3.  Example Token Exchange

   The following example demonstrates a hypothetical token exchange in
   which an OAuth resource server assumes the role of the client during
   token exchange in order to trade an access token that it received in
   a protected resource request for a token that it will use to call to
   a backend service (extra line breaks and indentation in the examples
   are for display purposes only).






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   The resource server receives the following request containing an
   OAuth access token in the Authorization request header, as specified
   in Section 2.1 of [RFC6750].

    GET /resource HTTP/1.1
    Host: frontend.example.com
    Authorization: Bearer accVkjcJyb4BWCxGsndESCJQbdFMogUC5PbRDqceLTC

                   Figure 1: Protected Resource Request

   The resource server assumes the role of the client for the token
   exchange and the access token from the request above is sent to the
   authorization server using a request as specified in Section 2.1.
   The value of the "subject_token" parameter carries the access token
   and the value of the "subject_token_type" parameter indicates that it
   is an OAuth 2.0 access token.  The resource server, acting in the
   role of the client, uses its identifier and secret to authenticate to
   the authorization server using the HTTP Basic authentication scheme.
   The "resource" parameter indicates the location of the backend
   service, https://backend.example.com/api, where the issued token will
   be used.

    POST /as/token.oauth2 HTTP/1.1
    Host: as.example.com
    Authorization: Basic cnMwODpsb25nLXNlY3VyZS1yYW5kb20tc2VjcmV0
    Content-Type: application/x-www-form-urlencoded

    grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
    &resource=https%3A%2F%2Fbackend.example.com%2Fapi%20
    &subject_token=accVkjcJyb4BWCxGsndESCJQbdFMogUC5PbRDqceLTC
    &subject_token_type=
     urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token

                     Figure 2: Token Exchange Request

   The authorization server validates the client credentials and the
   "subject_token" presented in the token exchange request.  From the
   "resource" parameter, the authorization server is able to determine
   the appropriate policy to apply to the request and issues a token
   suitable for use at https://backend.example.com.  The "access_token"
   parameter of the response contains the new token, which is itself a
   bearer OAuth access token that is valid for one minute.  The token
   happens to be a JWT; however, its structure and format are opaque to
   the client so the "issued_token_type" indicates only that it is an
   access token.






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    HTTP/1.1 200 OK
    Content-Type: application/json
    Cache-Control: no-cache, no-store

    {
     "access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjllciJ9.eyJhdWQiOiJo
       dHRwczovL2JhY2tlbmQuZXhhbXBsZS5jb20iLCJpc3MiOiJodHRwczovL2FzLmV
       4YW1wbGUuY29tIiwiZXhwIjoxNDQxOTE3NTkzLCJpYXQiOjE0NDE5MTc1MzMsIn
       N1YiI6ImJjQGV4YW1wbGUuY29tIiwic2NwIjpbImFwaSJdfQ.MXgnpvPMo0nhce
       PwnQbunD2gw_pDyCFA-Saobl6gyLAdyPbaALFuAOyFc4XTWaPEnHV_LGmXklSTp
       z0yC7hlSQ",
     "issued_token_type":
         "urn:ietf:params:oauth:token-type:access_token",
     "token_type":"Bearer",
     "expires_in":60
    }

                     Figure 3: Token Exchange Response

   The resource server can then use the newly acquired access token in
   making a request to the backend server.

    GET /api HTTP/1.1
    Host: backend.example.com
    Authorization: Bearer eyJhbGciOiJFUzI1NiIsImtpZCI6IjllciJ9.eyJhdWQ
       iOiJodHRwczovL2JhY2tlbmQuZXhhbXBsZS5jb20iLCJpc3MiOiJodHRwczovL2
       FzLmV4YW1wbGUuY29tIiwiZXhwIjoxNDQxOTE3NTkzLCJpYXQiOjE0NDE5MTc1M
       zMsInN1YiI6ImJjQGV4YW1wbGUuY29tIiwic2NwIjpbImFwaSJdfQ.MXgnpvPMo
       0nhcePwnQbunD2gw_pDyCFA-Saobl6gyLAdyPbaALFuAOyFc4XTWaPEnHV_LGmX
       klSTpz0yC7hlSQ

               Figure 4: Backend Protected Resource Request

   Additional examples can be found in Appendix A.

3.  Token Type Identifiers

   Several parameters in this specification utilize an identifier as the
   value to describe the token in question.  Specifically, they are the
   "requested_token_type", "subject_token_type", "actor_token_type"
   parameters of the request and the "issued_token_type" member of the
   response.  Token type identifiers are URIs.  Token Exchange can work
   with both tokens issued by other parties and tokens from the given
   authorization server.  For the former the token type identifier
   indicates the syntax (e.g., JWT or SAML 2.0) so the AS can parse it;
   for the latter it indicates what the AS issued it for (e.g.,
   access_token or refresh_token).




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   This specification defines the token type identifiers
   "urn:ietf:params:oauth:token-type:access_token" and
   "urn:ietf:params:oauth:token-type:refresh_token" to indicate that the
   token is an OAuth 2.0 access token or refresh token, respectively.
   The value "urn:ietf:params:oauth:token-type:jwt" defined in Section 9
   of [JWT] indicates that the token is a JWT.  This specification also
   defines the token type identifier "urn:ietf:params:oauth:token-
   type:id_token" to indicate that the token is an ID Token, as defined
   in Section 2 of [OpenID.Core].  Finally, this specification defines
   the token type identifiers "urn:ietf:params:oauth:token-type:saml1"
   and "urn:ietf:params:oauth:token-type:saml2" to indicate that the
   token is a base64url-encoded SAML 1.1 [OASIS.saml-core-1.1] or SAML
   2.0 [OASIS.saml-core-2.0-os] assertion, respectively.  Other URIs to
   indicate other token types MAY be used.

   The distinction between an access token and a JWT is subtle.  An
   access token represents a delegated authorization decision, whereas
   JWT is a token format.  An access token can be formatted as a JWT but
   doesn't necessarily have to be.  And a JWT might well be an access
   token but not all JWTs are access tokens.  The intent of this
   specification is that "urn:ietf:params:oauth:token-type:access_token"
   be an indicator that the token is a typical OAuth access token issued
   by the authorization server in question, opaque to the client, and
   usable the same manner as any other access token obtained from that
   authorization server.  (It could well be a JWT, but the client isn't
   and needn't be aware of that fact.)  Whereas,
   "urn:ietf:params:oauth:token-type:jwt" is to indicate specifically
   that a JWT is being requested or sent (perhaps in a cross-domain use-
   case where the JWT is used as an authorization grant to obtain an
   access token from a different authorization server as is facilitated
   by [RFC7523]).

4.  JSON Web Token Claims and Introspection Response Parameters

   It is useful to have defined mechanisms to express delegation within
   a token as well as to express authorization to delegate or
   impersonate.  Although the token exchange protocol described herein
   can be used with any type of token, this section defines claims to
   express such semantics specifically for JWTs and in an OAuth 2.0
   Token Introspection [RFC7662] response.  Similar definitions for
   other types of tokens are possible but beyond the scope of this
   specification.

4.1.  "act" (Actor) Claim

   The "act" (actor) claim provides a means within a JWT to express that
   delegation has occurred and identify the acting party to whom
   authority has been delegated.  The "act" claim value is a JSON object



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   and members in the JSON object are claims that identify the actor.
   The claims that make up the "act" claim identify and possibly provide
   additional information about the actor.  For example, the combination
   of the two claims "iss" and "sub" might be necessary to uniquely
   identify an actor.

   However, claims within the "act" claim pertain only to the identity
   of the actor and are not relevant to the validity of the containing
   JWT in the same manner as the top-level claims.  Consequently, non-
   identity claims (e.g., "exp", "nbf", and "aud") are not meaningful
   when used within an "act" claim, and therefore must not be used.

   The following example illustrates the "act" (actor) claim within a
   JWT Claims Set.  The claims of the token itself are about
   user@example.com while the "act" claim indicates that
   admin@example.com is the current actor.

    {
      "aud":"https://consumer.example.com",
      "iss":"https://issuer.example.com",
      "exp":1443904177,
      "nbf":1443904077,
      "sub":"user@example.com",
      "act":
      {
        "sub":"admin@example.com"
      }
    }

                           Figure 5: Actor Claim

   A chain of delegation can be expressed by nesting one "act" claim
   within another.  The outermost "act" claim represents the current
   actor while nested "act" claims represent prior actors.  The least
   recent actor is the most deeply nested.
















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   The following example illustrates nested "act" (actor) claims within
   a JWT Claims Set.  The claims of the token itself are about
   user@example.com while the "act" claim indicates that the system
   consumer.example.com-web-application is the current actor and
   admin@example.com was a prior actor.  Such a token might come about
   as the result of the web application receiving a token like the one
   in the previous example and exchanging it for a new token that lists
   it as the current actor and that can be used at
   https://backend.example.com.

    {
      "aud":"https://backend.example.com",
      "iss":"https://issuer.example.com",
      "exp":1443904100,
      "nbf":1443904000,
      "sub":"user@example.com",
      "act":
      {
        "sub":"consumer.example.com-web-application",
        "iss":"https://issuer.example.net",
        "act":
        {
          "sub":"admin@example.com"
        }
      }
    }

                       Figure 6: Nested Actor Claim

   When included as a top-level member of an OAuth token introspection
   response, "act" has the same semantics and format as the claim of the
   same name.

4.2.  "scp" (Scopes) Claim

   The "scp" claim is an array of strings, each of which represents an
   OAuth scope granted for the issued security token.  Each array entry
   of the claim value is a scope-token, as defined in Section 3.3 of
   OAuth 2.0 [RFC6749].












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   The following example illustrates the "scp" claim within a JWT Claims
   Set with four scope-tokens.

    {
      "aud":"https://consumer.example.com",
      "iss":"https://issuer.example.com",
      "exp":1443904177,
      "nbf":1443904077,
      "sub":"dgaf4mvfs75Fci_FL3heQA",
      "scp":["email","address","profile","phone"]
    }

                          Figure 7: Scopes Claim

   OAuth 2.0 Token Introspection [RFC7662] defines the "scope" parameter
   to convey the scopes associated with the token.

4.3.  "cid" (Client Identifier) Claim

   The "cid" claim carries the client identifier of the OAuth 2.0
   [RFC6749] client that requested the token.

   The following example illustrates the "cid" claim within a JWT Claims
   Set indicating an OAuth 2.0 client with "s6BhdRkqt3" as its
   identifier.

    {
      "aud":"https://consumer.example.com",
      "iss":"https://issuer.example.com",
      "exp":1443904177,
      "sub":"user@example.com",
      "cid":"s6BhdRkqt3"
    }

                     Figure 8: Client Identifier Claim

   OAuth 2.0 Token Introspection [RFC7662] defines the "client_id"
   parameter as the client identifier for the OAuth 2.0 client that
   requested the token.

4.4.  "may_act" (May Act For) Claim

   The "may_act" claim makes a statement that one party is authorized to
   become the actor and act on behalf of another party.  The claim value
   is a JSON object and members in the JSON object are claims that
   identify the party that is asserted as being eligible to act for the
   party identified by the JWT containing the claim.  The claims that
   make up the "may_act" claim identify and possibly provide additional



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   information about the authorized actor.  For example, the combination
   of the two claims "iss" and "sub" are sometimes necessary to uniquely
   identify an authorized actor, while the "email" claim might be used
   to provide additional useful information about that party.

   However, claims within the "may_act" claim pertain only to the
   identity of that party and are not relevant to the validity of the
   containing JWT in the same manner as top-level claims.  Consequently,
   claims such as "exp", "nbf", and "aud" are not meaningful when used
   within a "may_act" claim, and therefore should not be used.

   The following example illustrates the "may_act" claim within a JWT
   Claims Set.  The claims of the token itself are about
   user@example.com while the "may_act" claim indicates that
   admin@example.com is authorized to act on behalf of user@example.com.

    {
      "aud":"https://consumer.example.com",
      "iss":"https://issuer.example.com",
      "exp":1443904177,
      "nbf":1443904077,
      "sub":"user@example.com",
      "may_act":
      {
        "sub":"admin@example.com"
      }
    }

                        Figure 9: May Act For Claim

   When included as a top-level member of an OAuth token introspection
   response, "may_act" has the same semantics and format as the claim of
   the same name.

5.  IANA Considerations

5.1.  OAuth URI Registration

   This specification registers the following values in the IANA "OAuth
   URI" registry [IANA.OAuth.Parameters] established by [RFC6755].

5.1.1.  Registry Contents

   o  URN: urn:ietf:params:oauth:grant-type:token-exchange
   o  Common Name: Token exchange grant type for OAuth 2.0
   o  Change controller: IESG
   o  Specification Document: Section 2.1 of [[ this specification ]]




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   o  URN: urn:ietf:params:oauth:token-type:access_token
   o  Common Name: Token type URI for an OAuth 2.0 access token
   o  Change controller: IESG
   o  Specification Document: Section 3 of [[this specification]]

   o  URN: urn:ietf:params:oauth:token-type:refresh_token
   o  Common Name: Token type URI for an OAuth 2.0 refresh token
   o  Change controller: IESG
   o  Specification Document: Section 3 of [[this specification]]

   o  URN: urn:ietf:params:oauth:token-type:id_token
   o  Common Name: Token type URI for an ID Token
   o  Change controller: IESG
   o  Specification Document: Section 3 of [[this specification]]

   o  URN: urn:ietf:params:oauth:token-type:saml1
   o  Common Name: Token type URI for a base64url-encoded SAML 1.1
      assertion
   o  Change Controller: IESG
   o  Specification Document: Section 3 of [[this specification]]

   o  URN: urn:ietf:params:oauth:token-type:saml2
   o  Common Name: Token type URI for a base64url-encoded SAML 2.0
      assertion
   o  Change Controller: IESG
   o  Specification Document: Section 3 of [[this specification]]

5.2.  OAuth Parameters Registration

   This specification registers the following values in the IANA "OAuth
   Parameters" registry [IANA.OAuth.Parameters] established by
   [RFC6749].

5.2.1.  Registry Contents

   o  Parameter name: resource
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: audience
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: requested_token_type
   o  Parameter usage location: token request
   o  Change controller: IESG



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   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: subject_token
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: subject_token_type
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: actor_token
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: actor_token_type
   o  Parameter usage location: token request
   o  Change controller: IESG
   o  Specification document(s): Section 2.1 of [[ this specification ]]

   o  Parameter name: issued_token_type
   o  Parameter usage location: token response
   o  Change controller: IESG
   o  Specification document(s): Section 2.2.1 of [[ this specification
      ]]

5.3.  OAuth Access Token Type Registration

   This specification registers the following access token type in the
   IANA "OAuth Access Token Types" registry [IANA.OAuth.Parameters]
   established by [RFC6749].

5.3.1.  Registry Contents

   o  Type name: N_A
   o  Additional Token Endpoint Response Parameters: (none)
   o  HTTP Authentication Scheme(s): (none)
   o  Change controller: IESG
   o  Specification document(s): Section 2.2.1 of [[ this specification
      ]]

5.4.  JSON Web Token Claims Registration

   This specification registers the following Claims in the IANA "JSON
   Web Token Claims" registry [IANA.JWT.Claims] established by [JWT].




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5.4.1.  Registry Contents

   o  Claim Name: "act"
   o  Claim Description: Actor
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.1 of [[ this specification ]]

   o  Claim Name: "scp"
   o  Claim Description: Scope Values
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.2 of [[ this specification ]]

   o  Claim Name: "cid"
   o  Claim Description: Client Identifier
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.3 of [[ this specification ]]

   o  Claim Name: "may_act"
   o  Claim Description: May Act For
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.4 of [[ this specification ]]

5.5.  OAuth Token Introspection Response Registration

   This specification registers the following values in the IANA "OAuth
   Token Introspection Response" registry [IANA.OAuth.Parameters]
   established by [RFC7662].

5.5.1.  Registry Contents

   o  Claim Name: "act"
   o  Claim Description: Actor
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.1 of [[ this specification ]]

   o  Claim Name: "may_act"
   o  Claim Description: May Act For
   o  Change Controller: IESG
   o  Specification Document(s): Section 4.4 of [[ this specification ]]

5.6.  OAuth Extensions Error Registration

   This specification registers the following values in the IANA "OAuth
   Extensions Error" registry [IANA.OAuth.Parameters] established by
   [RFC6749].






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5.6.1.  Registry Contents

   o  Error Name: "invalid_target"
   o  Error Usage Location: token error response
   o  Related Protocol Extension: OAuth 2.0 Token Exchange
   o  Change Controller: IETF
   o  Specification Document(s): Section 2.2.2 of [[ this specification
      ]]

6.  Security Considerations

   All of the normal security issues that are discussed in [JWT],
   especially in relationship to comparing URIs and dealing with
   unrecognized values, also apply here.

   In addition, both delegation and impersonation introduce unique
   security issues.  Any time one principal is delegated the rights of
   another principal, the potential for abuse is a concern.  The use of
   the "scp" claim is suggested to mitigate potential for such abuse, as
   it restricts the contexts in which the delegated rights can be
   exercised.

7.  Privacy Considerations

   Tokens typically carry personal information and their usage in Token
   Exchange may reveal details of the target services being accessed.
   As such, tokens should only be requested and sent according to the
   privacy policies at the respective organizations.

8.  References

8.1.  Normative References

   [IANA.JWT.Claims]
              IANA, "JSON Web Token Claims",
              <http://www.iana.org/assignments/jwt>.

   [IANA.OAuth.Parameters]
              IANA, "OAuth Parameters",
              <http://www.iana.org/assignments/oauth-parameters>.

   [JWT]      Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://tools.ietf.org/html/rfc7519>.







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   [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>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [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>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

   [RFC7662]  Richer, J., Ed., "OAuth 2.0 Token Introspection",
              RFC 7662, DOI 10.17487/RFC7662, October 2015,
              <https://www.rfc-editor.org/info/rfc7662>.

8.2.  Informative References

   [OASIS.saml-core-1.1]
              Maler, E., Mishra, P., and R. Philpott, "Assertions and
              Protocol for the OASIS Security Assertion Markup Language
              (SAML) V1.1", OASIS Standard oasis-sstc-saml-core-1.1,
              September 2003.

   [OASIS.saml-core-2.0-os]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005.

   [OpenID.Core]
              Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0", August 2015,
              <http://openid.net/specs/openid-connect-core-1_0.html>.

   [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>.






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   [RFC6755]  Campbell, B. and H. Tschofenig, "An IETF URN Sub-Namespace
              for OAuth", RFC 6755, DOI 10.17487/RFC6755, October 2012,
              <https://www.rfc-editor.org/info/rfc6755>.

   [RFC7521]  Campbell, B., Mortimore, C., Jones, M., and Y. Goland,
              "Assertion Framework for OAuth 2.0 Client Authentication
              and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521,
              May 2015, <https://www.rfc-editor.org/info/rfc7521>.

   [RFC7523]  Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token
              (JWT) Profile for OAuth 2.0 Client Authentication and
              Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May
              2015, <https://www.rfc-editor.org/info/rfc7523>.

   [WS-Trust]
              Nadalin, A., Goodner, M., Gudgin, M., Barbir, A., and H.
              Granqvist, "WS-Trust 1.4", February 2012,
              <http://docs.oasis-open.org/ws-sx/ws-trust/v1.4/
              ws-trust.html>.

Appendix A.  Additional Token Exchange Examples

   Two example token exchanges are provided in the following sections
   illustrating impersonation and delegation, respectively (with extra
   line breaks and indentation for display purposes only).

A.1.  Impersonation Token Exchange Example

A.1.1.  Token Exchange Request

   In the following token exchange request, a client is requesting a
   token with impersonation semantics.  The client tells the
   authorization server that it needs a token for use at the target
   service with the logical name "urn:example:cooperation-context".

















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    POST /as/token.oauth2 HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
    &audience=urn%3Aexample%3Acooperation-context
    &subject_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwc
      zovL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXI
      uZXhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTA2MDAsIm5iZiI6MTQ0MTkwOTAwMCwic
      3ViIjoiYmNAZXhhbXBsZS5uZXQiLCJzY3AiOlsib3JkZXJzIiwicHJvZmlsZSIsImh
      pc3RvcnkiXX0.JDe7fZ267iIRXwbFmOugyCt5dmGoy6EeuzNQ3MqDek5cCUlyPhQC6
      cz9laKjK1bnjMQbLJqWix6ZdBI0isjsTA
    &subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt

                     Figure 10: Token Exchange Request

A.1.2.  Subject Token Claims

   The "subject_token" in the prior request is a JWT and the decoded JWT
   Claims Set is shown here.  The JWT is intended for consumption by the
   authorization server within a specific time window.  The subject of
   the JWT ("bc@example.net") is the party on behalf of whom the new
   token is being requested.

     {
       "aud":"https://as.example.com",
       "iss":"https://original-issuer.example.net",
       "exp":1441910600,
       "nbf":1441909000,
       "sub":"bc@example.net",
       "scp":["orders","profile","history"]
     }

                      Figure 11: Subject Token Claims

A.1.3.  Token Exchange Response

   The "access_token" parameter of the token exchange response shown
   below contains the new token that the client requested.  The other
   parameters of the response indicate that the token is a bearer access
   token that expires in an hour.










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    HTTP/1.1 200 OK
    Content-Type: application/json
    Cache-Control: no-cache, no-store

    {
     "access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjcyIn0.eyJhdWQiOiJ1cm4
       6ZXhhbXBsZTpjb29wZXJhdGlvbi1jb250ZXh0IiwiaXNzIjoiaHR0cHM6Ly9hcy5l
       eGFtcGxlLmNvbSIsImV4cCI6MTQ0MTkxMzYxMCwic3ViIjoiYmNAZXhhbXBsZS5uZ
       XQiLCJzY3AiOlsib3JkZXJzIiwiaGlzdG9yeSIsInByb2ZpbGUiXX0.YQHuLmI1YD
       TugbfEvgGY2gaGBmMyj9BepZSECCBE9j9ogqZv2qx6VQQPrbT1k7vBYGLNMOkkpmm
       JkxZDS0YV7g",
     "issued_token_type":
       "urn:ietf:params:oauth:token-type:access_token",
     "token_type":"Bearer",
     "expires_in":3600
    }

                    Figure 12: Token Exchange Response

A.1.4.  Issued Token Claims

   The decoded JWT Claims Set of the issued token is shown below.  The
   new JWT is issued by the authorization server and intended for
   consumption by a system entity known by the logical name
   "urn:example:cooperation-context" any time before its expiration.
   The subject ("sub") of the JWT is the same as the subject the token
   used to make the request, which effectively enables the client to
   impersonate that subject at the system entity known by the logical
   name of "urn:example:cooperation-context" by using the token.

     {
       "aud":"urn:example:cooperation-context",
       "iss":"https://as.example.com",
       "exp":1441913610,
       "sub":"bc@example.net",
       "scp":["orders","history","profile"]
     }

                      Figure 13: Issued Token Claims

A.2.  Delegation Token Exchange Example

A.2.1.  Token Exchange Request

   In the following token exchange request, a client is requesting a
   token and providing both a "subject_token" and an "actor_token".  The
   client tells the authorization server that it needs a token for use
   at the target service with the logical name "urn:example:cooperation-



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   context".  Policy at the authorization server dictates that the
   issued token be a composite.

    POST /as/token.oauth2 HTTP/1.1
    Host: as.example.com
    Content-Type: application/x-www-form-urlencoded

    grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
    &audience=urn%3Aexample%3Acooperation-context
    &subject_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwc
      zovL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXI
      uZXhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInNjcCI6WyJzdGF0dXMiLCJmZ
      WVkIl0sInN1YiI6InVzZXJAZXhhbXBsZS5uZXQiLCJtYXlfYWN0Ijp7InN1YiI6ImF
      kbWluQGV4YW1wbGUubmV0In19.ut0Ll7wm920VzRvuLGLFoPJLeO5DDElxsax1L_xK
      Um2eooiNSfuif-OGa2382hPyFYnddKIa0wmDhQksW018Rw
    &subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt
    &actor_token=eyJhbGciOiJFUzI1NiIsImtpZCI6IjE2In0.eyJhdWQiOiJodHRwczo
      vL2FzLmV4YW1wbGUuY29tIiwiaXNzIjoiaHR0cHM6Ly9vcmlnaW5hbC1pc3N1ZXIuZ
      XhhbXBsZS5uZXQiLCJleHAiOjE0NDE5MTAwNjAsInN1YiI6ImFkbWluQGV4YW1wbGU
      ubmV0In0.7YQ-3zPfhUvzje5oqw8COCvN5uP6NsKik9CVV6cAOf4QKgM-tKfiOwcgZ
      oUuDL2tEs6tqPlcBlMjiSzEjm3yBg
    &actor_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Ajwt

                     Figure 14: Token Exchange Request

A.2.2.  Subject Token Claims

   The "subject_token" in the prior request is a JWT and the decoded JWT
   Claims Set is shown here.  The JWT is intended for consumption by the
   authorization server before a specific expiration time.  The subject
   of the JWT ("user@example.net") is the party on behalf of whom the
   new token is being requested.

     {
       "aud":"https://as.example.com",
       "iss":"https://original-issuer.example.net",
       "exp":1441910060,
       "scp":["status","feed"],
       "sub":"user@example.net",
       "may_act":
       {
         "sub":"admin@example.net"
       }
     }

                      Figure 15: Subject Token Claims





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A.2.3.  Actor Token Claims

   The "actor_token" in the prior request is a JWT and the decoded JWT
   Claims Set is shown here.  This JWT is also intended for consumption
   by the authorization server before a specific expiration time.  The
   subject of the JWT ("admin@example.net") is the actor that will wield
   the security token being requested.

     {
       "aud":"https://as.example.com",
       "iss":"https://original-issuer.example.net",
       "exp":1441910060,
       "sub":"admin@example.net"
     }

                       Figure 16: Actor Token Claims

A.2.4.  Token Exchange Response

   The "access_token" parameter of the token exchange response shown
   below contains the new token that the client requested.  The other
   parameters of the response indicate that the token is a JWT that
   expires in an hour and that the access token type is not applicable
   since the issued token is not an access token.

    HTTP/1.1 200 OK
    Content-Type: application/json
    Cache-Control: no-cache, no-store

    {
     "access_token":"eyJhbGciOiJFUzI1NiIsImtpZCI6IjcyIn0.eyJhdWQiOiJ1cm4
       6ZXhhbXBsZTpjb29wZXJhdGlvbi1jb250ZXh0IiwiaXNzIjoiaHR0cHM6Ly9hcy5l
       eGFtcGxlLmNvbSIsImV4cCI6MTQ0MTkxMzYxMCwic2NwIjpbInN0YXR1cyIsImZlZ
       WQiXSwic3ViIjoidXNlckBleGFtcGxlLm5ldCIsImFjdCI6eyJzdWIiOiJhZG1pbk
       BleGFtcGxlLm5ldCJ9fQ._qjM7Ij_HcrC78omT4jiZTFJOuzsAj1wPo31ymQS-Suq
       r64S1jCp6pfQR-in_OOAosAGamEg4jyPsht6kMAiYA",
     "issued_token_type":"urn:ietf:params:oauth:token-type:jwt",
     "token_type":"N_A",
     "expires_in":3600
    }

                    Figure 17: Token Exchange Response

A.2.5.  Issued Token Claims

   The decoded JWT Claims Set of the issued token is shown below.  The
   new JWT is issued by the authorization server and intended for
   consumption by a system entity known by the logical name



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   "urn:example:cooperation-context" any time before its expiration.
   The subject ("sub") of the JWT is the same as the subject of the
   "subject_token" used to make the request.  The actor ("act") of the
   JWT is the same as the subject of the "actor_token" used to make the
   request.  This indicates delegation and identifies
   "admin@example.net" as the current actor to whom authority has been
   delegated to act on behalf of "user@example.net".

     {
       "aud":"urn:example:cooperation-context",
       "iss":"https://as.example.com",
       "exp":1441913610,
       "scp":["status","feed"],
       "sub":"user@example.net",
       "act":
       {
         "sub":"admin@example.net"
       }
     }

                      Figure 18: Issued Token Claims

Appendix B.  Acknowledgements

   This specification was developed within the OAuth Working Group,
   which includes dozens of active and dedicated participants.  It was
   produced under the chairmanship of Hannes Tschofenig and Derek Atkins
   with Kathleen Moriarty and Stephen Farrell serving as Security Area
   Directors.  The following individuals contributed ideas, feedback,
   and wording to this specification:

   Caleb Baker, Vittorio Bertocci, Thomas Broyer, William Denniss,
   Vladimir Dzhuvinov, Phil Hunt, Benjamin Kaduk, Jason Keglovitz,
   Torsten Lodderstedt, Adam Lewis, James Manger, Nov Matake, Matt
   Miller, Matthew Perry, Justin Richer, Rifaat Shekh-Yusef, Scott
   Tomilson, and Hannes Tschofenig.

Appendix C.  Document History

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   -10

   o  Defined token type URIs for base64url-encoded SAML 1.1 and SAML
      2.0 assertions.
   o  Applied editorial fixes.

   -09



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   o  Changed "security tokens obtained could be used in a number of
      contexts" to "security tokens obtained may be used in a number of
      contexts" per a WGLC suggestion.
   o  Clarified that the validity of the subject or actor token have no
      impact on the validity of the issued token after the exchange has
      occurred per a WGLC comment.
   o  Changed use of invalid_target error code to a SHOULD per a WGLC
      comment.
   o  Clarified text about non-identity claims within the "act" claim
      being meaningless per a WGLC comment.
   o  Added brief Privacy Considerations section per WGLC comments.

   -08

   o  Use the bibxml reference for OpenID.Core rather than defining it
      inline.
   o  Added editor role for Campbell.
   o  Minor clarification of the text for actor_token.

   -07

   o  Fixed typo (desecration -> discretion).
   o  Added an explanation of the relationship between scope, audience
      and resource in the request and added an "invalid_target" error
      code enabling the AS to tell the client that the requested
      audiences/resources were too broad.

   -06

   o  Drop "An STS for the REST of Us" from the title.
   o  Drop "heavyweight" and "lightweight" from the abstract and
      introduction.
   o  Clarifications on the language around xxxxxx_token_type.
   o  Remove the want_composite parameter.
   o  Add a short mention of proof-of-possession style tokens to the
      introduction and remove the respective open issue.

   -05

   o  Defined the JWT claim "cid" to express the OAuth 2.0 client
      identifier of the client that requested the token.
   o  Defined and requested registration for "act" and "may_act" as
      Token introspection response parameters (in addition to being JWT
      claims).
   o  Loosen up the language about refresh_token in the response to
      OPTIONAL from NOT RECOMMENDED based on feedback form real world
      deployment experience.




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   o  Add clarifying text about the distinction between JWT and access
      token URIs.
   o  Close out (remove) some of the Open Issues bullets that have been
      resolved.

   -04

   o  Clarified that the "resource" and "audience" request parameters
      can be used at the same time (via http://www.ietf.org/mail-
      archive/web/oauth/current/msg15335.html).
   o  Clarified subject/actor token validity after token exchange and
      explained a bit more about the recommendation to not issue refresh
      tokens (via http://www.ietf.org/mail-archive/web/oauth/current/
      msg15318.html).
   o  Updated the examples appendix to use an issuer value that doesn't
      imply that the client issued and signed the tokens and used
      "Bearer" and "urn:ietf:params:oauth:token-type:access_token" in
      one of the responses (via http://www.ietf.org/mail-
      archive/web/oauth/current/msg15335.html).
   o  Defined and registered urn:ietf:params:oauth:token-type:id_token,
      since some use cases perform token exchanges for ID Tokens and no
      URI to indicate that a token is an ID Token had previously been
      defined.

   -03

   o  Updated the document editors (adding Campbell, Bradley, and
      Mortimore).
   o  Added to the title.
   o  Added to the abstract and introduction.
   o  Updated the format of the request to use application/x-www-form-
      urlencoded request parameters and the response to use the existing
      token endpoint JSON parameters defined in OAuth 2.0.
   o  Changed the grant type identifier to urn:ietf:params:oauth:grant-
      type:token-exchange.
   o  Added RFC 6755 registration requests for
      urn:ietf:params:oauth:token-type:refresh_token,
      urn:ietf:params:oauth:token-type:access_token, and
      urn:ietf:params:oauth:grant-type:token-exchange.
   o  Added RFC 6749 registration requests for request/response
      parameters.
   o  Removed the Implementation Considerations and the requirement to
      support JWTs.
   o  Clarified many aspects of the text.
   o  Changed "on_behalf_of" to "subject_token",
      "on_behalf_of_token_type" to "subject_token_type", "act_as" to
      "actor_token", and "act_as_token_type" to "actor_token_type".




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   o  Added an "audience" request parameter used to indicate the logical
      names of the target services at which the client intends to use
      the requested security token.
   o  Added a "want_composite" request parameter used to indicate the
      desire for a composite token rather than trying to infer it from
      the presence/absence of token(s) in the request.
   o  Added a "resource" request parameter used to indicate the URLs of
      resources at which the client intends to use the requested
      security token.
   o  Specified that multiple "audience" and "resource" request
      parameter values may be used.
   o  Defined the JWT claim "act" (actor) to express the current actor
      or delegation principal.
   o  Defined the JWT claim "may_act" to express that one party is
      authorized to act on behalf of another party.
   o  Defined the JWT claim "scp" (scopes) to express OAuth 2.0 scope-
      token values.
   o  Added the "N_A" (not applicable) OAuth Access Token Type
      definition for use in contexts in which the token exchange syntax
      requires a "token_type" value, but in which the token being issued
      is not an access token.
   o  Added examples.

   -02

   o  Enabled use of Security Token types other than JWTs for "act_as"
      and "on_behalf_of" request values.
   o  Referenced the JWT and OAuth Assertions RFCs.

   -01

   o  Updated references.

   -00

   o  Created initial working group draft from draft-jones-oauth-token-
      exchange-01.

Authors' Addresses

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/






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   Anthony Nadalin
   Microsoft

   Email: tonynad@microsoft.com


   Brian Campbell (editor)
   Ping Identity

   Email: brian.d.campbell@gmail.com


   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com


   Chuck Mortimore
   Salesforce

   Email: cmortimore@salesforce.com





























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