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Versions: 00 01 02 03

Network Working Group                                     J. Richer, Ed.
Internet-Draft                                       Bespoke Engineering
Intended status: Standards Track                        November 1, 2019
Expires: May 4, 2020


                      Transactional Authorization
                  draft-richer-transactional-authz-03

Abstract

   This document defines a mechanism for delegating authorization to a
   piece of software, and conveying that delegation to the software.

Requirements Language

   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 RFC 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they
   appear in all capitals, as shown here.

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 May 4, 2020.

Copyright Notice

   Copyright (c) 2019 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



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   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.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Parties . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Sequence  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Transaction request . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Display . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Resource  . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.3.  User  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.4.  Interact  . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.5.  Keys  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  Interaction response  . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Redirect interaction  . . . . . . . . . . . . . . . . . .  11
     3.2.  Interaction URI return  . . . . . . . . . . . . . . . . .  12
     3.3.  Calculating the interaction hash  . . . . . . . . . . . .  14
     3.4.  Secondary device interaction  . . . . . . . . . . . . . .  14
   4.  Wait response . . . . . . . . . . . . . . . . . . . . . . . .  15
   5.  Interaction at the AS . . . . . . . . . . . . . . . . . . . .  16
   6.  Error response  . . . . . . . . . . . . . . . . . . . . . . .  16
   7.  Transaction continue request  . . . . . . . . . . . . . . . .  17
   8.  Token response  . . . . . . . . . . . . . . . . . . . . . . .  18
     8.1.  Presenting Tokens to the RS . . . . . . . . . . . . . . .  18
   9.  Handle references . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Presenting handles  . . . . . . . . . . . . . . . . . . .  19
     9.2.  Validating handles  . . . . . . . . . . . . . . . . . . .  19
     9.3.  Transaction handles . . . . . . . . . . . . . . . . . . .  19
     9.4.  Display handles . . . . . . . . . . . . . . . . . . . . .  20
     9.5.  Resource handles  . . . . . . . . . . . . . . . . . . . .  20
       9.5.1.  Resource-first  . . . . . . . . . . . . . . . . . . .  22
     9.6.  User handles  . . . . . . . . . . . . . . . . . . . . . .  22
     9.7.  Key handles . . . . . . . . . . . . . . . . . . . . . . .  23
   10. Binding Keys  . . . . . . . . . . . . . . . . . . . . . . . .  24
     10.1.  Detached JWS . . . . . . . . . . . . . . . . . . . . . .  24
     10.2.  Mutual TLS . . . . . . . . . . . . . . . . . . . . . . .  25
     10.3.  DPoP . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     10.4.  HTTP Signing . . . . . . . . . . . . . . . . . . . . . .  25
     10.5.  OAuth PoP  . . . . . . . . . . . . . . . . . . . . . . .  25
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  26
   14. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  26
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  26



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   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  28
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Protocol

   This protocol allows a piece of software to request delegated
   authorization to an API, protected by an authorization server usually
   on behalf of a resource owner.

1.1.  Parties

   The Authorization Server (AS) manages the transactions.  It is
   defined by its transaction endpoint, a single URL that accepts a POST
   request with a JSON payload.  The AS MAY also have other endpoints,
   including interaction endpoints and user code endpoints, and these
   are introduced to the RC as needed during the transaction process.

   The Resource Client (RC) requests tokens from the AS and uses tokens
   at the RS.

   The Resource Server (RS) accepts tokens from the RC and validates
   them (potentially at the AS).

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

1.2.  Sequence

   1.  The RC creates a transaction request and sends it to the AS

   2.  The AS processes the transaction request and determines if the RO
       needs to interact

   3.  If interaction is required, the AS interacts with the RO,
       possibly by directing the RC to send the RO there

   4.  The RC continues the transaction at the AS

   5.  The AS processes the transaction again, determining that a token
       can be issued

   6.  The AS issues a token to the RC

   7.  The RC uses the token with the RS







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2.  Transaction request

   To start a transaction, the RC makes a transaction request to the
   transaction endpoint of the AS.  The RC creates a JSON [RFC8259]
   document with five primary sections, included as members of a root
   JSON object.

   resources  Information about the RS's the resulting token will be
      applied to, including locations, extents of access, types of data
      being accessed, and other API information.  This section is
      REQUIRED.

   keys  Information about the keys known to the RC and able to be
      presented in future parts of the transaction.  This section is
      REQUIRED.  (Note: I can't think of a good reason for this to be
      optional.)

   interact  Information about how the RC is able to interact with the
      RO, including callback URI's and nonce if applicable.  This
      section is REQUIRED if the RC is capable of driving interaction
      with the user.

   display  Information about the RC making the request, including
      display name, home page, logo, and other user-facing information.
      This section is RECOMMENDED.

   user  Information about the RO as known to or provided to the RC, in
      the form of assertions or references to external data.  This
      section is OPTIONAL.

   Each section consists of either a JSON object or an array of JSON
   objects, as described in the subsections below.  Many sections MAY be
   represented by an appropriate handle instead as described in
   Section 9.  In such cases, the section is replaced entirely by the
   handle presentation, which is a single string instead of a JSON
   object.  The RC MAY present additional sections as defined by
   extensions of this specification.  The AS MUST ignore any sections
   that it does not understand.

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











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   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata"
       ],
       "key": {
           "proof": "jwsd",
           "jwks": {
               "keys": [
                   {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeL...."
                   }
               ]
           }
       },
       "interact": {
           "redirect": true,
           "callback": {
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       }
   }






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2.1.  Display

   This section provides descriptive details of the RC software making
   the call, useful for displaying information about the client to the
   user during the authorization request.  This section is a JSON
   object, and all fields are OPTIONAL.  The RC MAY send additional
   fields, and the AS MUST ignore all fields that it does not
   understand.

   name  Display name of the RC software

   uri  User-facing web page of the RC software

   logo_uri  Display image to represent the RC software

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

   The AS SHOULD use this information in presenting any authorization
   screens to the RO during interaction.

   The display information MAY instead be presented as a display handle
   reference Section 9.4.

2.2.  Resource

   This section identifies what the RC wants to do with the API hosted
   at the RS.  This section is a JSON array of objects, each object
   representing a single resource or resource set.  That AS MUST
   interpret the request as being for all of the resources listed.

   actions  The types of actions the RC will take at the RS

   locations  URIs the RC will call at the RS

   datatypes  types of data available to the RC at the RS's API













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

   This can also be presented as a set of resource handle references
   Section 9.5, or a combination of handles and resource structures.

2.3.  User

   This section provides a verifiable assertion about the person
   interacting with the RC on behalf of the request.  This person MAY be
   the RO or MAY be another party.

   assertion  The value of the assertion as a string.

   type  The type of the assertion.  Possible values include
      "oidc_id_token"...

    "user": {
        "assertion": "eyJraWQiOiIxZTlnZGs3IiwiYWxnIjoiUlMyNTYifQ.ewogImlzcyI6ICJodHRwOi8vc2VydmVyLmV4YW1wbGUuY29tIiwKICJzdWIiOiAiMjQ4Mjg5NzYxMDAxIiwKICJhdWQiOiAiczZCaGRSa3F0MyIsCiAibm9uY2UiOiAibi0wUzZfV3pBMk1qIiwKICJleHAiOiAxMzExMjgxOTcwLAogImlhdCI6IDEzMTEyODA5NzAsCiAibmFtZSI6ICJKYW5lIERvZSIsCiAiZ2l2ZW5fbmFtZSI6ICJKYW5lIiwKICJmYW1pbHlfbmFtZSI6ICJEb2UiLAogImdlbmRlciI6ICJmZW1hbGUiLAogImJpcnRoZGF0ZSI6ICIwMDAwLTEwLTMxIiwKICJlbWFpbCI6ICJqYW5lZG9lQGV4YW1wbGUuY29tIiwKICJwaWN0dXJlIjogImh0dHA6Ly9leGFtcGxlLmNvbS9qYW5lZG9lL21lLmpwZyIKfQ.rHQjEmBqn9Jre0OLykYNnspA10Qql2rvx4FsD00jwlB0Sym4NzpgvPKsDjn_wMkHxcp6CilPcoKrWHcipR2iAjzLvDNAReF97zoJqq880ZD1bwY82JDauCXELVR9O6_B0w3K-E7yM2macAAgNCUwtik6SjoSUZRcf-O5lygIyLENx882p6MtmwaL1hd6qn5RZOQ0TLrOYu0532g9Exxcm-ChymrB4xLykpDj3lUivJt63eEGGN6DH5K6o33TcxkIjNrCD4XB1CKKumZvCedgHHF3IAK4dVEDSUoGlH9z4pP_eWYNXvqQOjGs-rDaQzUHl6cQQWNiDpWOl_lxXjQEvQ",
        "type": "oidc_id_token"
    }

   This can also be presented as a user handle reference Section 9.6.

2.4.  Interact

   This section provides details of how the RC can interact with the RO.
   All fields are OPTIONAL, and the RC MAY include multiple possible
   interaction modes.  If a field is not present, it is interpreted as
   negative support for that feature.





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   callback  If this object is present, it indicates the RC is capable
      of receiving inbound messages from the RO's browser in response to
      user interaction.  This object contains the following fields:

      uri  REQUIRED.  Indicates the URI to send the RO to after
         interaction.  This URI MAY be unique per transaction and MUST
         be hosted 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 user'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 encode that into the callback
         URI.  The allowable URIs and URI patterns MAY be limited 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.

      nonce  REQUIRED.  Unique value to be used in the calculation of
         the "hash" query parameter on 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 transaction.

   redirect  If this is set to true, the RC is capable of redirecting
      the RO to an arbitrary interaction URL as described in Section 5.
      The RC MAY communicate the URI to the user through a browser
      redirection, a QR code, or some other mechanism.

   user_code  If this is set to true, the RC is capable of displaying a
      short user code to the user and directing them to a fixed URL as
      descrbed in Section 5.

   didcomm  If this is set to true, the RC is capable of relaying a
      DIDComm message to an agent or wallet.

   didcomm_query  If this is set to true, the RC is capable of relaying
      a DIDComm query to an agent or wallet.

   This section MUST NOT be represented by a handle reference.  (Note:
   this decision is largely due to the "callback" section being variable
   per transaction.  We could allow a handle but restrict it to non-
   callback methods -- but in that case, it's simpler and shorter to
   just send the booleans instead of having a special case.)

   The following example is from an RC that can redirect to the
   interaction endpoint and receive returns on a callback URI:






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   "interact": {
       "redirect": true,
       "callback": {
           "uri": "https://example.com/client/123456",
           "nonce": "VJLO6A4CAYLBXHTR0KRO"
       }
   }

2.5.  Keys

   This section lists the keys that the RC can present proof of
   ownership.  The RC MUST send at least one key.  The RC MAY send more
   than one key format, but all keys MUST be equivalent.

   proof  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 10.  This field is
      REQUIRED.

   jwks  Value of the public key as a JWK Set JSON object [Note: should
      this be a single JWK instead?  And do we want to bother with url-
      based references?].  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  PEM serialized value of the certificate used for TLS
      transactions, with optional internal whitespace.

   cert#256  The certificate thumbprint calculated as per OAuth-MTLS
      [I-D.ietf-oauth-mtls].

   did  The DID URL identifying the key (or keys) used to sign this
      request.

   The RC MUST provide proof of possession of all presented
   keysSection 10.  All presented keys MUST be validated by the AS using
   the method defined by proof.

   This section MAY also be presented as a key handle reference
   Section 9.7.  The keys referenced by a handle MUST be validated by
   the AS.

   The following non-normative example shows three key types, with the
   detached JWS proofing mechanism:







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    "keys": {
        "proof": "jwsd",
        "jwks": {
            "keys": [
                {
                    "kty": "RSA",
                    "e": "AQAB",
                    "kid": "xyz-1",
                    "alg": "RS256",
                    "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xY..."
                }
            ]
        },
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFA...",
        "did": "did:example:CV3BVVXK2PWWLCRQLRFU#xyz-1"
    }

3.  Interaction response

   When evaluating a transaction request, the AS MAY determine that it
   needs to have the RO present to interact with the AS before issuing a
   token.  This interaction can include the RO logging in to the AS,
   authorizing the transaction, providing proof claims, determining if
   the transaction decision should be remembered for the future, and
   other items.

   The AS responds to the RC based on the type of interaction supported
   by the RC in the transaction request.  The AS MAY respond with
   mutliple possible interaction methods to be chosen by the RC.  For
   example, if the RC indicates that it can handle redirects and user
   codes and has a callback URI, it would send a transaction request
   like this:



















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   {
       "interact": {
           "redirect": true,
           "user_code": true,
           "callback": {
               "uri": "https://client.example.net/return/123455",
               "nonce": "LKLTI25DK82FX4T4QFZC"
           }
       },
       "resources": [
           "dolphin-metadata"
       ],
       "key": "7C7C4AZ9KHRS6X63AJAO",
       "display": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       }
   }

   The AS would then respond with a transaction response like this:

{
    "interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
    "server_nonce": "MBDOFXG4Y5CVJCX821LH",
    "user_code": {
        "url": "https://server.example.com/interact/device",
        "code": "A1BC-3DFF"
    },
    "handle": {
        "value": "80UPRY5NM33OMUKMKSKU",
        "type": "bearer"
    }
}

   This response MUST include a transaction handle as described in
   Section 9.3 so that the transaction can continue after the user has
   interacted.

3.1.  Redirect interaction

   If the RC supports a "redirect" style interaction, the AS creates a
   unique interaction URL and returns it to the RC.  This URL MUST be
   associated with the current transaction and no other transaction.

   interaction_url  REQUIRED.  The interaction URL that the RC will
      direct the RO to.  This URL MUST be unique to this transaction
      request.  The URL SHOULD contain a random portion of sufficient
      entropy so as not to be guessable by the user.  The URL MUST NOT



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      contain the transaction handle or any RC identifying information.
      This URL MUST be protected by HTTPS.  This URL MUST NOT contain
      any fragment component.

   handle  REQUIRED.  The transaction handle to use in the continue the
      transaction Section 7.

{
    "interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
    "handle": {
        "value": "80UPRY5NM33OMUKMKSKU",
        "type": "bearer"
    }
}

   When the RC receives this response, it MUST launch the system
   browser, redirect the RO through an HTTP 302 response, display the
   URL through a scannable barcode, or otherwise send the RO to the
   interaction URL.  The RC MUST NOT modify the interaction URL or
   append anything to it, including any query parameters, fragments, or
   special headers.

   The interaction URL MUST be reachable from the RO's browser, though
   note that the RO MAY open the interaction 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.

   Upon receiving an incoming request at the interaction URL, the AS
   MUST determine the transaction associated with this unique URL.  If
   the transaction is not found, an error is returned to the end user
   through the browser and the AS MUST NOT attempt to redirect to a
   callback URL.  When interacting with the RO, the AS MAY perform any
   of the behaviors in the User Interaction section Section 5.

3.2.  Interaction URI return

   If the RC has supplied a callback URL in its interact request
   Section 2.4, the AS returns a nonce in its interaction response.

   server_nonce  REQUIRED.  A unique value from the server included in
      the calculation of the "hash" value returned in the callback
      response.  REQUIRED if the client has sent a "callback" parameter
      in its interaction request.

   This example also includes the interaction URL from Section 3.1.






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{
    "interaction_url": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
    "server_nonce": "MBDOFXG4Y5CVJCX821LH",
    "handle": {
        "value": "80UPRY5NM33OMUKMKSKU",
        "type": "bearer"
    }
}

   When interaction has concluded, the AS returns the user to the RC by
   redirecting the RO's browser to the RC's callback URL presented at
   the start of the transaction, with the addition of two query
   parameters.

   hash  REQUIRED.  The interaction hash value as described in
      Section 3.3.

   interact_handle  REQUIRED.  A shared secret associated with this
      interaction.  This value MUST be sufficiently random so as not to
      be guessable by an attacker.  This value MUST be associated by the
      AS with the underlying transaction that is associated to with this
      interaction.

   The AS MUST properly process the callback parameter from the
   interaction request as a URL, adding these values as query
   parameters.  The AS MUST NOT use simple string concatentation.  For
   example, for the callback URL of "https://example.com/client/123456",
   the AS would add query parameters as follows (newlines added for
   display purposes only):

https://example.com/client/123456
  ?hash=p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
  &interact_handle=4IFWWIKYBC2PQ6U56NL1

   Upon processing this request to the callback URL, the RC MUST
   calculate the expected value of the "hash" parameter as described in
   Section 3.3 and compare that value to the "hash" parameter on the
   incoming request.  The RC then sends a transaction continuation
   request with the transaction handle returned in the interaction
   response and the (hash of?) the interaction handle returned as a
   query parameter to the callback URL.

   The RC sends (the hash of? example here is hashed) the interaction
   handle as the "interact_handle" field of the transaction continuation
   requestSection 7, using the transaction handle Section 9.3 returned
   in the most recent transaction response from the AS.





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{
    "handle": "80UPRY5NM33OMUKMKSKU",
    "interact_handle": "CuD9MrpSXVKvvI6dN1awtNLx-HhZy46hJFDBicG4KoZaCmBofvqPxtm7CDMTsUFuvcmLwi_zUN70cCvalI6ENw"
}

3.3.  Calculating the interaction hash

   The "hash" parameter in the interaction response ties the front
   channel response to a transaction by using values known only to the
   parties in the transaction.  To calculate the "hash" value for the
   interaction response, the party doing the calculation first takes the
   "nonce" value sent by the RC in the interaction section of the
   initial transaction request Section 2.4, the "server_nonce" value
   returned in the transaction response Section 3.2, and the
   "interact_handle" returned in the callback response Section 3.2.
   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 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

3.4.  Secondary device interaction

   If the RC supports a "user_code" style interaction, the AS creates a
   unique user interaction code and returns it to the RC.  The RC
   communicates this code to the RO and instructs the RO to enter the
   code at a URL hosted by the AS.

   user_code  REQUIRED.  An object containing the user code information.

      user_code  REQUIRED.  A 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.

      user_code_url  RECOMMENDED.  The interaction URL that the RC will
         direct the RO to.  This URL SHOULD be stable at the AS such
         that clients can be statically configured with it.



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   wait  RECOMMENDED.  The amount of time to wait before polling again,
      in integer seconds.  If not specified, the default is 30 seconds.
      See Section 4.

   handle  REQUIRED.  The transaction handle to use in the continue
      request.  See the section on transaction handlesSection 9.3.

   {
       "user_code": {
           "url": "https://server.example.com/interact/device",
           "code": "A1BC-3DFF"
       },
       "wait": 30,
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       }
   }

   When the RC receives this response, it MUST communicate the user code
   to the RO.  If possible the RC SHOULD communicate the interaction URL
   to the user as well.  However, the URL is generally understood to be
   stable over time for a given service, and this URL MAY be
   communicated through a static means such as the device's
   documentation or packaging.

   When the RO enters the unique user code at the user code URL, the AS
   MUST determine which active transaction is associated with the user
   code.  If a transaction is not found, the AS MUST return an error
   page to the user and MUST NOT attempt to redirect to a callback URL.
   The AS MAY use any mechanism to interact with the RO as listed in
   Section 5.

   Note that this method is strictly for allowing the user to enter a
   code at a static URL.  If the AS wishes to communicate a pre-composed
   URL to the RO containing both the user code and the URL at which to
   enter it, the AS MUST use the "interaction_url" Section 3.1 redirect
   mechanism instead as this allows the client to communicate an
   arbitrary interaction URL to the RO.

4.  Wait response

   If the AS needs the RC to wait before it can give a definitive
   response to a transaction continue requestSection 7, the AS replies
   to the transaction request with a wait response.  This tells the RC
   that it can poll the transaction after a set amount of time.





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   This response includes a transaction handle as in Transaction Handle
   Section 9.3.

   wait  REQUIRED.  The amount of time to wait before polling again, in
      integer seconds.

   handle  REQUIRED.  The transaction handle to use in the continue
      request.  This MUST be a newly-created handle and MUST replace any
      existing handle for this transaction.  See the section on
      transaction handles.

   {
       "wait": 30,
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       }
   }

5.  Interaction at the AS

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

   o  authenticate the RO

   o  gather identity claims about the RO

   o  gather consent and authorization from the RO

   o  allow the RO to modify the parameters of the requested transaction
      (such as disallowing some requested resources)

   When the AS has concluded interacting with the RO, the AS MUST
   determine if the RC has registered a callback URL and nonce parameter
   for this transaction.  If so, the AS MUST redirect the RO's browser
   to the callback URL as described in Section 3.  If the AS detects an
   error condition, such as an unknown transaction, an untrustworthy
   callback URL, an untrustworthy client, or suspicious RO behavior, the
   AS MUST return an error to the RO's browser and MUST NOT redirect to
   the callback URL.

6.  Error response

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




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   include a transaction handle, and the RC can no longer poll for this
   transaction.  The RC MAY create a new transaction and start again.

   error  The error code.

   {

     "error": "user_denied"

   }

   TODO: we should have a more robust error mechanism.  Current
   candidate list of errors:

   user_denied  The RO denied the transaction request.

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

   unknown_transaction  The transaction continuation request referenced
      an unknown transaction.

   unknown_handle  The request referenced an unknown handle.

7.  Transaction continue request

   Once a transaction has begun, the AS associates that transaction with
   a transaction handleSection 9.3 which is returned to the RC in one of
   the transaction responses Section 3.1, Section 3.4, Section 4.  This
   handle MUST be unique, MUST be associated with a single transaction,
   and MUST be one time use.

   The RC continues the transaction by making a request with the
   transaction handle in the body of the request.  The RC MAY add
   additional fields to the transaction continuation request, such as
   the interaction handle return in the callback response Section 3.

   handle  REQUIRED.  The (hash of?) transaction handle indicating which
      transaction to continue.

   interaction_handle  OPTIONAL.  If the RC has received an interaction
      handle from the callback response of the interaction URL, the RC
      MUST include the (hash of?) that handle in its transaction
      continue request.








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   {

     "handle": "tghji76ytghj9876tghjko987yh"

   }

   The RC MUST prove all keys initially sent in the transaction
   requestSection 2.5 as described in Section 10.

   [[ Note: should we allowe the client to mutate the transaction at
   this point?  We already allow the presentation of the interaction
   handle, and any messaging protocols like DIDComm would allow
   additional work to be done here.  But do we want the client to be
   able to specify additional resources, or new interaction methods, or
   anything like that?  I'm inclined not to so that's been left out for
   now. ]]

8.  Token response

   access_token  The access token that the RC uses to call the RS.  The
      access token follows the handle structure described in Section 9.

   handle  The transaction handle to use in the continue
      requestSection 7 to get a new access token once the one issued is
      no longer usable.  See the section on transaction
      handlesSection 9.3.

   {
       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "type": "bearer"
       },
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       }
   }

8.1.  Presenting Tokens to the RS

   A bearer style access token MUST be presented using the Header method
   of OAuth 2 Bearer Tokens [RFC6750].  A sha3 style access token is
   hashed as described in Section 9.1 and presented using the Header
   method of OAuth 2 Bearer Tokens [RFC6750].

   An access token MAY be bound to any keys presented by the client
   during the transaction request.  A bound access token MUST be
   presented with proof of the key as described in Section 10.



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9.  Handle references

   A handle in this protocol is a value presented from one party to
   another as proof that they are the appropriate party for part of the
   transaction.  Handles can be used to reference the transaction as a
   whole, or one of its constituent parts.  When a handle is used to
   represent a part of a transaction request, the handle presentation
   replaces the original value.  In practical terms, this often means
   that the values of a transaction request are either an object (when
   the full value is used) or a single string (when the handle is used).

   value  The value of the handle as a string.

   method  The verification method, MUST be one of "bearer" or "sha3".

9.1.  Presenting handles

   Bearer handles are presented by giving the exact string value of the
   handle in the appropriate place.

   SHA3 handles are validated by taking the SHA3 hash of the handle
   value and encoding it in Base64URL with no padding, and presenting
   the encoded value.

9.2.  Validating handles

   Bearer handles are validated by doing an exact byte comparison of the
   string representation of the handle value.

   SHA3 handles are validated by taking the SHA3 hash of the handle
   value and encoding it in Base64URL with no padding, and comparing
   that using an exact byte comparison with the presented value.

9.3.  Transaction handles

   Transaction handles are issued by the AS to the RC to allow the RC to
   continue a transaction after every step.  A transaction handle MUST
   be discarded after it is used by both the AS and the RC.  A
   transaction MUST have only a single handle associated with it at any
   time.  If the AS determines that the RC can still continue the
   transaction after a handle has been used, a new transaction handle
   will be issued in its place.  If the AS does not issue a transaction
   handle in its response to the RC, the RC MUST NOT continue that
   transaction.

   Transaction handles always represent the current state of the
   transaction which they reference.




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   Transactions can be continued by the RC if the AS needs to interact
   with the ROSection 5 and the RC is expecting a callbackSection 3 or
   if the AS is still waiting on some external conditionSection 4 while
   the RC is polling.  The transaction MAY also be continued after an
   access token is issued Section 8 as a means of refreshing an access
   token with the same rights associated with the transaction.

9.4.  Display handles

   RC handles stand in for the display section of the initial
   transaction requestSection 2.1.  The AS MAY issue a display handle to
   a RC as part of a static registration process, analogous to a client
   ID in OAuth 2, allowing the RC to be associated with an AS-side
   configuration that does not change at runtime.  Such static processes
   SHOULD be bound to a set of keys known only to the RC software.

   Display handles MAY be issued by the RS in response to a transaction
   request.  The AS MAY associate the display handle to the interact,
   resource, and key handles issued in the same response, requiring them
   to be used together.  When the RC receives this handle, it MAY
   present the handle in future transaction requests instead of sending
   its information again.

   {
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       },
       "display_handle": {
           "value": "VBUEOIQA82PBY2ZDJW7Q",
           "type": "bearer"
       }
   }

   The RC sends its handle in lieu of the display block of the
   transaction request:

   {

     "display": "absc2948afgdkjnasdf9082ur3kjasdfasdf89"

   }

9.5.  Resource handles

   Resource handles stand in for the detailed resource request in the
   transaction requestSection 2.2.  Resource handles MAY be created by




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   the authorization server as static stand-ins for specific resource
   requests, analogous to OAuth2 scopes.

   Resource handles MAY be issued by the RS in response to a transaction
   request.  In such cases, the resource handle returned represents the
   total of all resources

   {
       "wait": 30,
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       },
       "resources_handle": {
           "value": "KLKP36N7GPOKRF3KGH5N",
           "type": "bearer"
       }
   }

   The RC sends its handle in lieu of the resource block of the future
   transaction request:

   {

     "resources": ["KLKP36N7GPOKRF3KGH5N"]

   }

   Note that handles and object values MAY be combined in a single
   request.





















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   {
       "resources": [
           {
               "actions": [
                   "read",
                   "write",
                   "dolphin"
               ],
               "locations": [
                   "https://server.example.net/",
                   "https://resource.local/other"
               ],
               "datatypes": [
                   "metadata",
                   "images"
               ]
           },
           "dolphin-metadata",
           "KLKP36N7GPOKRF3KGH5N"
       ]
   }

9.5.1.  Resource-first

   [[ Strawman idea: ]]

   In order to facilitate dynamic API protection, an RS MAY pre-register
   a resource handle in response to an unauthorized request from the RC.
   In this scenario, the RS creates a transaction request with no client
   information but describing the resources being protected [[Note: this
   is currently at odds with the required format above, perhaps this
   should be a special mode or flag?  We could still use the "keys"
   section here though.]] The AS returns a resource handle to the RS,
   which then communicates both the resource handle and the AS
   transaction endpoint to the RC.  The RC then begins its transaction
   as normal, using the resource handle as one of perhaps several
   resources it requests.

9.6.  User handles

   User handles MAY be issued by the AS in response to validating a
   specific RO during a transaction and stand in for the user section of
   a transaction requestSection 2.3.  This handle MAY refer to the RO
   that interacted with the AS, the user presented by claims in the
   transaction request, or a combination of these.  This handle can be
   used in future transactions to represent the current user, analogous
   to the persistent claims token of UMA 2.




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   {
       "wait": 30,
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       },
       "user_handle": {
           "value": "XUT2MFM1XBIKJKSDU8QM",
           "type": "bearer"
       }
   }

   The RC sends its handle in lieu of the user block of the transaction
   request:

   {

     "user": "XUT2MFM1XBIKJKSDU8QM"

   }

9.7.  Key handles

   Key handles stand in for the keys section of the initial transaction
   requestSection 2.5.  The AS MAY issue a key handle to a RC as part of
   a static registration process, allowing the RC to be associated with
   an AS-side configuration that does not change at runtime.

   Key handles MAY be issued by the AS in response to a transaction
   request.  The AS SHOULD bind this handle to the display, resource,
   and user handles issued in the same response.  When the RC receives
   this handle, it MAY present the handle in future transaction requests
   instead of sending its information again.

   {
       "wait": 30,
       "handle": {
           "value": "80UPRY5NM33OMUKMKSKU",
           "type": "bearer"
       },
       "key_handle": {
           "value": "7C7C4AZ9KHRS6X63AJAO",
           "type": "bearer"
       }
   }

   The RC sends its handle in lieu of the keys block of the transaction
   request:



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   {

     "keys": "7C7C4AZ9KHRS6X63AJAO"

   }

   When the AS receives a key handle, it MUST validate that the keys
   referenced by the handle are bound to the current transaction request
   using the proof method referenced by the handle.

10.  Binding Keys

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

   jwsd  A detached JWS signature header

   mtls  Mutual TLS certificate verification

   dpop  OAuth DPoP key proof header

   httpsig  HTTP Signing signature header

   oauthpop  OAuth PoP key proof authentication header

   Additional values can be defined by a registry.

   All keys presented by the RC in the transaction requestSection 2 MUST
   be proved in all transaction continuation requestsSection 7 for that
   transaction.  The AS MUST validate all keys presented by the RC or
   referenced in the transaction at each call to the transaction
   endpoint.  The client MUST NOT use a different key during the
   transaction.

10.1.  Detached JWS

   This method is indicated by "jwsd" in the "proof" field of a key
   request.  To sign a request to the transaction endpoint, the RC takes
   the serialized body of the request and signs it using detached JWS
   [RFC7797].  The header of the JWS MUST contain the kid field of the
   key bound to this RC during this transaction.  The JWS header MUST
   contain an alg field appropriate for the key identified by kid and
   MUST NOT be none.





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   The RC presents the signature in the JWS-Signature HTTP Header field.
   [Note: this is a custom header field, do we need this?]

   JWS-Signature: eyj0....

   When the AS receives the JWS-Signature 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.

10.2.  Mutual TLS

   This method is indicated by "mtls" in the "proof" field of a key
   request.  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 [I-D.ietf-oauth-mtls] section
   3.

10.3.  DPoP

   This method is indicated by "dpop" in the "proof" field of a key
   request.  The RC creates a DPoP signature header as described in
   [I-D.fett-oauth-dpop] section 2.

10.4.  HTTP Signing

   This method is indicated by "httpsig" in the "proof" field of a key
   request.  The RC creates an HTTP Signature header as described in
   [I-D.cavage-http-signatures] section 4.  The RC MUST calculate and
   present the Digest header as defined in [RFC3230].

10.5.  OAuth PoP

   This method is indicated by "oauthpop" in the "proof" field of a key
   request.  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:

   o  The at (access token) field MUST be omitted [note: this is in
      contrast to the requirements in the existing spec]

   o  The b (body hash) field MUST be calculated and supplied








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11.  Acknowledgements

12.  IANA Considerations

   [We'll want a registry for key proof types, and maybe some other
   field names.  We'll need to register at least one header and maybe
   some others?]

13.  Security Considerations

   All requests have to be over TLS or equivalent.  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

   Handles are passed between parties and therefore should be stateful
   and not contain any internal structure or information, which could
   leak private data.

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)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/bcp195>.

   [I-D.cavage-http-signatures]
              Cavage, M. and M. Sporny, "Signing HTTP Messages", draft-
              cavage-http-signatures-12 (work in progress), October
              2019.

   [I-D.fett-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)",
              draft-fett-oauth-dpop-03 (work in progress), October 2019.

   [I-D.ietf-oauth-mtls]
              Campbell, B., Bradley, J., Sakimura, N., and T.
              Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
              and Certificate-Bound Access Tokens", draft-ietf-oauth-
              mtls-17 (work in progress), August 2019.







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   [I-D.ietf-oauth-signed-http-request]
              Richer, J., Bradley, J., and H. Tschofenig, "A Method for
              Signing HTTP Requests for OAuth", draft-ietf-oauth-signed-
              http-request-03 (work in progress), August 2016.

   [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>.

   [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>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

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

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.



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Appendix A.  Document History

   - 03

   o  Removed "state" in favor of "nonce".

   o  Created signed return parameter for front channel return.

   o  Changed "client" section to "display" section, as well as
      associated handle.

   o  Changed "key" to "keys".

   o  Separated key proofing from key presentation.

   o  Separated interaction methods into booleans instead of "type"
      field.

   - 02

   o  Minor editorial cleanups.

   - 01

   o  Made JSON multimodal for handle requests.

   o  Major updates to normative language and references throughout
      document.

   o  Allowed interaction to split between how the user gets to the AS
      and how the user gets back.

   - 00

   o  Initial submission.

Author's Address

   Justin Richer (editor)
   Bespoke Engineering

   Email: ietf@justin.richer.org









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