XYZ: Grant Negotiation Access Protocol
draft-richer-transactional-authz-10

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Author Justin Richer 
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GNAP                                                      J. Richer, Ed.
Internet-Draft                                       Bespoke Engineering
Intended status: Standards Track                        2 September 2020
Expires: 6 March 2021

                 XYZ: Grant Negotiation Access Protocol
                  draft-richer-transactional-authz-10

Abstract

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

   This document is input into the GNAP working group and should be
   referred to as "XYZ" to differentiate it from other proposals.

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

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 6 March 2021.

Copyright Notice

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

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

Table of Contents

   1.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Roles . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Sequences . . . . . . . . . . . . . . . . . . . . . . . .   4
       1.2.1.  Redirect-based Interaction  . . . . . . . . . . . . .   6
       1.2.2.  User-code-based Interaction . . . . . . . . . . . . .   8
       1.2.3.  Asynchronous Authorization  . . . . . . . . . . . . .  10
       1.2.4.  Software-only Authorization . . . . . . . . . . . . .  12
       1.2.5.  Refreshing an Expired Access Token  . . . . . . . . .  13
   2.  Requesting Access . . . . . . . . . . . . . . . . . . . . . .  14
     2.1.  Requesting Resources  . . . . . . . . . . . . . . . . . .  15
       2.1.1.  Requesting a Single Access Token  . . . . . . . . . .  15
       2.1.2.  Requesting Resources By Reference . . . . . . . . . .  16
       2.1.3.  Requesting Multiple Access Tokens . . . . . . . . . .  18
     2.2.  Requesting User Information . . . . . . . . . . . . . . .  19
     2.3.  Identifying the Client Key  . . . . . . . . . . . . . . .  20
       2.3.1.  Authenticating the Client . . . . . . . . . . . . . .  21
       2.3.2.  Identifying the Client Key By Reference . . . . . . .  22
     2.4.  Identifying the User  . . . . . . . . . . . . . . . . . .  22
       2.4.1.  Identifying the User by Reference . . . . . . . . . .  23
     2.5.  Interacting with the User . . . . . . . . . . . . . . . .  24
       2.5.1.  Redirect to an Arbitrary URL  . . . . . . . . . . . .  25
       2.5.2.  Open an Application-specific URL  . . . . . . . . . .  26
       2.5.3.  Receive a Callback After Interaction  . . . . . . . .  26
       2.5.4.  Display a Short User Code . . . . . . . . . . . . . .  28
       2.5.5.  Extending Interaction Capabilities  . . . . . . . . .  28
     2.6.  Providing Displayable Client Information  . . . . . . . .  29
     2.7.  Declaring Client Capabilities . . . . . . . . . . . . . .  29
     2.8.  Referencing an Existing Grant Request . . . . . . . . . .  30
     2.9.  Requesting OpenID Connect Claims  . . . . . . . . . . . .  30
     2.10. Extending The Grant Request . . . . . . . . . . . . . . .  31
   3.  Grant Response  . . . . . . . . . . . . . . . . . . . . . . .  31
     3.1.  Request Continuation Handle . . . . . . . . . . . . . . .  32
     3.2.  Access Tokens . . . . . . . . . . . . . . . . . . . . . .  33
       3.2.1.  Single Access Token . . . . . . . . . . . . . . . . .  33
       3.2.2.  Multiple Access Tokens  . . . . . . . . . . . . . . .  34
     3.3.  Interaction Capabilities  . . . . . . . . . . . . . . . .  35
       3.3.1.  Redirection to an arbitrary URL . . . . . . . . . . .  35

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       3.3.2.  Launch of an application URL  . . . . . . . . . . . .  36
       3.3.3.  Callback to a Client URL  . . . . . . . . . . . . . .  36
       3.3.4.  Display of a Short User Code  . . . . . . . . . . . .  37
       3.3.5.  Extending Interaction Capability Responses  . . . . .  38
     3.4.  Returning User Information  . . . . . . . . . . . . . . .  38
     3.5.  Returning Dynamically-bound Reference Handles . . . . . .  39
     3.6.  Error response  . . . . . . . . . . . . . . . . . . . . .  40
     3.7.  Extending the Response  . . . . . . . . . . . . . . . . .  40
   4.  Interaction at the AS . . . . . . . . . . . . . . . . . . . .  40
     4.1.  Interaction at a Redirected URI . . . . . . . . . . . . .  41
     4.2.  Interaction at the User Code URI  . . . . . . . . . . . .  41
     4.3.  Interaction through an Application URI  . . . . . . . . .  42
     4.4.  Post-Interaction Completion . . . . . . . . . . . . . . .  42
       4.4.1.  Completing Interaction with a Callback URI  . . . . .  43
       4.4.2.  Completing Interaction with a Pushback URI  . . . . .  43
       4.4.3.  Calculating the interaction hash  . . . . . . . . . .  44
   5.  Continuing a Grant Request  . . . . . . . . . . . . . . . . .  45
     5.1.  Continuing after a Finalized Interaction  . . . . . . . .  46
     5.2.  Continuing after Tokens are Issued  . . . . . . . . . . .  46
   6.  Token Management  . . . . . . . . . . . . . . . . . . . . . .  47
     6.1.  Rotating the Access Token . . . . . . . . . . . . . . . .  47
     6.2.  Revoking the Access Token . . . . . . . . . . . . . . . .  48
   7.  Using Access Tokens . . . . . . . . . . . . . . . . . . . . .  49
   8.  Binding Keys  . . . . . . . . . . . . . . . . . . . . . . . .  49
     8.1.  Detached JWS  . . . . . . . . . . . . . . . . . . . . . .  50
     8.2.  Attached JWS  . . . . . . . . . . . . . . . . . . . . . .  52
     8.3.  Mutual TLS  . . . . . . . . . . . . . . . . . . . . . . .  54
     8.4.  DPoP  . . . . . . . . . . . . . . . . . . . . . . . . . .  55
     8.5.  HTTP Signing  . . . . . . . . . . . . . . . . . . . . . .  57
     8.6.  OAuth PoP . . . . . . . . . . . . . . . . . . . . . . . .  58
   9.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . .  59
   10. Resource Servers  . . . . . . . . . . . . . . . . . . . . . .  60
     10.1.  Introspecting a Token  . . . . . . . . . . . . . . . . .  61
     10.2.  Deriving a downstream token  . . . . . . . . . . . . . .  62
     10.3.  Registering a Resource Handle  . . . . . . . . . . . . .  63
     10.4.  Requesting a Resources With Insufficient Access  . . . .  65
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  65
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  65
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  66
   14. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  66
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  66
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  68
   Appendix B.  Component Data Models  . . . . . . . . . . . . . . .  70
   Appendix C.  Example Protocol Flows . . . . . . . . . . . . . . .  70
     C.1.  Redirect-Based User Interaction . . . . . . . . . . . . .  71
     C.2.  Secondary Device Interaction  . . . . . . . . . . . . . .  75
   Appendix D.  No User Involvement  . . . . . . . . . . . . . . . .  77
     D.1.  Asynchronous Authorization  . . . . . . . . . . . . . . .  78

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     D.2.  Applying OAuth 2 Scopes and Client IDs  . . . . . . . . .  81
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  82

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.  The user operating the software may
   interact with the authorization server to authenticate, provide
   consent, and authorize the request.

   The process by which the delegation happens is known as a grant, and
   the GNAP protocol allows for the negotiation of the grant process
   over time by multiple parties

1.1.  Roles

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

   The Resource Client (RC, aka "client") requests tokens from the AS
   and uses tokens at the RS.  The RC is identified by its key, and can
   be known to the AS prior to the first request.  The AS determines
   which policies apply to a given client.

   The Resource Server (RS) accepts tokens from the RC and validates
   them (potentially at the AS).  The RS serves delegated resources on
   behalf of the RO.

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

   The Requesting Party (RQ, aka "user") operates the RC and may be the
   same party as the RO in many circumstances.

1.2.  Sequences

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

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   Note that a connection between roles in this process does not
   necessarily indicate that a specific protocol message is sent across
   the wire between the components fulfilling the roles in question, or
   that a particular step is required every time.  In some
   circumstances, the information needed at a given stage is
   communicated out-of-band or is pre-configured between the components
   or entities performing the roles.  For example, one entity can fulfil
   multiple roles, and so explicit communication between the roles is
   not necessary within the protocol flow.

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

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

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

   *  (1) The RC attempts to call the RS (Section 10.4) to determine
      what access is needed.  The RS informs the RC that access can be
      granted through the AS.

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

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

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

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

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

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

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

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

1.2.1.  Redirect-based Interaction

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

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

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

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

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

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

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

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

   7.  When the AS is done interacting with the user, the AS redirects
       the user back (Section 4.4.1) to the RC using the callback URL
       provided in (2).  The callback URL is augmented with an
       interaction reference that the AS associates with the ongoing
       request created in (2) and referenced in (4).  The callback URL
       is also augmented with a hash of the security information
       provided in (2) and (3).  The RC loads the verification
       information from (2) and (3) from the session created in (1).
       The RC calculates a hash (Section 4.4.3) based on this
       information and continues only if the hash validates.

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

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

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

1.2.2.  User-code-based Interaction

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

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

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

   2.   The AS determines that interaction is needed and responds
        (Section 3) with a user code to communicate to the user
        (Section 3.3.4).  This could optionally include a URL to direct
        the user to, but this URL should be static and so could be
        configured in the RC's documentation.  The AS also includes
        information the RC will need to continue the request
        (Section 3.1) in (8) and (10).  The AS associates this
        continuation information with an ongoing request that will be
        referenced in (4), (6), (8), and (10).

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

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   4.   The user's directs their browser to the user code URL.  This URL
        is stable and can be communicated via the client's
        documentation, the AS documentation, or the client software
        itself.  The client does not provide a mechanism to launch the
        user's browser at this URL.  The user enters the code
        communicated in (3) to the AS.  The AS validates this code
        against a current request in process.

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

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

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

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

   9.   If the access request has not yet been authorized by the RO in
        (6), the AS responds to the RC to continue the request
        (Section 3.1) at a future time through additional polling.  This
        response can include refreshed credentials as well as
        information regarding how long the RC should wait before calling
        again.  The RC replaces its stored continuation information from
        the previous response (2).

   10.  The RC continues to poll the AS (Section 5) with the new
        continuation information in (9).

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

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

1.2.3.  Asynchronous Authorization

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

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

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

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

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

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

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

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

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

   8.  The RC continues to poll the AS (Section 5) with the new
       continuation information in (7).

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

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

1.2.4.  Software-only Authorization

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

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

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

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

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

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1.2.5.  Refreshing an Expired Access Token

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

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

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

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

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

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

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

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

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2.  Requesting Access

   To start a request, the client sends JSON [RFC8259] document with an
   object as its root.  Each member of the request object represents a
   different aspect of the client's request.

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

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

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           "uri": "https://example.net/client"
       },
       "capabilities": ["ext1", "ext2"],
       "subject": {
           "sub_ids": ["iss-sub", "email"],
           "assertions": ["oidc_id_token"]
       }
   }

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

2.1.  Requesting Resources

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

2.1.1.  Requesting a Single Access Token

   When requesting a single access token, the client MUST send a
   resources element containing a JSON array.  The elements of the JSON
   array represent rights of access that the client is requesting in the
   access token.  The requested access is the sum of all elements within
   the array.  These request elements MAY be sent by value as an object
   or by reference as a string.  A single resources array MAY contain
   both object and string type resource requests.

   The client declares what access it wants to associated with the
   resulting access token using objects that describe multiple
   dimensions of access.  Each object contains a "type" property that
   determines the type of API that the client is calling.  The value of
   this field is under the control of the AS and it MAY determine which
   other fields allowed in the object.  While it is expected that many
   APIs will have its own properties, a set of common properties are
   defined here.  Specific API implementations SHOULD NOT re-use these
   fields with different semantics or syntax.

   [[ Editor's note: this will align with OAuth 2 RAR, but the details
   of how it aligns are TBD ]].

   actions  The types of actions the RC will take at the RS as an array
      of strings.  The values of the strings are determined by the API
      being protected.

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   locations  The location of the RS as an array of strings.  These
      strings are typically URIs, and are determined by the API being
      protected.

   datatypes  Kinds of data available to the RC at the RS's API as an
      array of strings.  The values of the strings are determined by the
      API being protected.

   identifier  A string identifier indicating a specific resource at the
      RS.  The value of the string is determined by the API being
      protected.

   The following non-normative example shows the use of both common and
   API-specific elements.

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

2.1.2.  Requesting Resources By Reference

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

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   [[ Editor's note: we could describe more about how the expansion
   would work.  For example, expand into an object where the value of
   the "type" field is the value of the string.  Or we could leave it
   open and flexible, since it's really up to the AS/RS to interpret. ]]

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

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

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

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

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

2.1.3.  Requesting Multiple Access Tokens

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

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

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

2.2.  Requesting User Information

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

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

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   assertions  An array of requested assertion formats defined by a
      registry TBD (Section 12).

   "subject": {
      "sub_ids": [ "iss-sub", "email" ],
      "assertions": [ "oidc-id-token", "saml" ]
   }

   If the AS knows the identifier for the current user and has
   permission to do so [[ editor's note: from the user's consent or data
   policy or ... ]], the AS MAY return the user's information in its
   response (Section 3.4).

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

   [[ Editor's note: we're potentially conflating these two fields in
   the same structure, so perhaps these should be split.  There's also a
   difference between user information and authentication event
   information. ]]

2.3.  Identifying the Client Key

   When sending an initial request to the AS, the client MUST identify
   itself by including the key field in the request and by signing the
   request as described in Section 8.  This key MAY be sent by value or
   by reference.

   When sent by value, the key MUST be a public key in at least one
   supported format and MUST contain a proof property that matches the
   proofing mechanism used in the request.  If the key is sent in
   multiple formats, all the keys MUST be the same.  The key presented
   in this field MUST be the key used to sign the request.

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

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

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

   cert#256  The certificate thumbprint calculated as per OAuth-MTLS

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      [RFC8705] in base64 URL encoding.

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

   [[ Editor's note: we will eventually want to have fetchable keys, I
   would guess.  Things like DID for key identification are going to be
   important. ]]

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

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

   The RC MUST prove possession of any presented key by the "proof"
   mechanism associated with the key in the request.  Proof types are
   defined in a registry TBD (Section 12) and an initial set are of
   methods are described in Section 8.  Continuation requests
   (Section 5) MUST use the same key and proof method as the initial
   request.

   [[ Editor's note: additional client attestation frameworks will
   eventually need to be addressed here beyond the presentation of the
   key.  For example, the organization the client represents, or a
   family of client software deployed in a cluster, or the posture of
   the device the client is installed on.  These all need to be
   separable from the client's key and the key identifier. ]]

2.3.1.  Authenticating the Client

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

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   The presentation of a key is of vital importance to the protocol as
   it allows the AS to strongly associate multiple requests from the
   same RC with each other.  This value exists whether the AS knows the
   key ahead of time or not, and as such the AS MAY allow for clients to
   make requests with unknown keys.  This pattern allows for ephemeral
   clients, such as single-page applications, and many-instance clients,
   such as mobile applications, to generate their own key pairs and use
   them within the protocol without having to go through a separate
   registration step.  The AS MAY limit which capabilities are made
   available to clients with unknown keys.  For example, the AS could
   have a policy saying that only previously-registered clients can
   request particular resources.

2.3.2.  Identifying the Client Key By Reference

   If the client has a reference for its key, the client MAY send that
   reference handle as a string.  The format of this string is opaque to
   the client.

   {
     "key": "7C7C4AZ9KHRS6X63AJAO"
   }

   If the key is passed by reference, the proofing mechanism associated
   with that key reference MUST also be used by the client, as described
   in Section 8.

   If the AS does not recognize the key reference handle, the request
   MUST be rejected with an error.

   If the client identifies its key by reference, the referenced key MAY
   be a symmetric key known to the AS.  The client MUST NOT send a
   symmetric key by value, as doing so would be a security violation.

   [[ Editor's note: In many ways, passing a key identifier by reference
   is analogous to OAuth 2's "client_id" parameter [RFC6749], especially
   when coupled with a confidential client's authentication process.
   See Appendix D.2 for an example. ]]

2.4.  Identifying the User

   If the client knows the identity of the current user or one or more
   identifiers for the user, the client MAY send that information to the
   AS in the "user" field.  The client MAY pass this information by
   value or by reference.

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

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   assertions  An object containing assertions as values keyed on the
      assertion type defined by a registry TBD (Section 12). [[ Editor's
      note: should this be an array of objects with internal typing like
      the sub_ids?  Do we expect more than one assertion per user
      anyway? ]]

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

   Subject identifiers are hints to the AS in determining the current
   user and MUST NOT be taken as declarative statements that a
   particular user is present at the client.  Assertions SHOULD be
   validated by the AS. [[ editor's note: assertion validation is
   extremely specific to the kind of assertion in place ]]

   If the identified user does not match the user present at the AS
   during an interaction step, the AS SHOULD reject the request.

   [[ Editor's note: we're potentially conflating identification
   (sub_ids) and provable presence (assertions and a trusted reference
   handle) in the same structure, so perhaps these should be split. ]]

   Additional user assertion formats are defined in a registry TBD
   (Section 12). [[ Editor's note: probably the same registry as
   requesting formats to keep them aligned. ]]

   If the AS trusts the client to present user information, it MAY
   decide, based on its policy, to skip interaction with the user, even
   if the client provides one or more interaction capabilities.

2.4.1.  Identifying the User by Reference

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

   "user": "XUT2MFM1XBIKJKSDU8QM"

   User reference identifiers are not intended to be human-readable user
   identifiers or machine-readable verifiable assertions.  For either of
   these, use the regular user request instead.

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

2.5.  Interacting with the User

   If the client is capable of driving interaction with the user, the
   client SHOULD declare the means that it can interact using the
   "interact" field.  This field is a JSON object with keys that declare
   different interaction capabilities.  A client MUST NOT declare an
   interaction capability it does not support.

   The client MAY send multiple capabilities in the same request.  There
   is no preference order specified in this request.  An AS MAY respond
   to any, all, or none of the presented interaction capabilities
   (Section 3.3) in a request, depending on its capabilities and what is
   allowed to fulfill the request.

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

   [[ Editor's note: there need to be more examples (Appendix C) that
   knit together the interaction capabilities into common flows, like an
   authz-code equivalent.  But it's important for the protocol design
   that these are separate pieces to allow such knitting to take place.
   ]]

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

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

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2.5.1.  Redirect to an Arbitrary URL

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

   "interact": {
      "redirect": true
   }

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

2.5.1.1.  Redirect to an Arbitrary Shortened URL

   If the client would prefer to redirect to a shortened URL defined by
   the AS at runtime, the client indicates this by sending the
   "redirect" field with an integer indicating the maximum character
   length of the returned URL.  The AS MAY use this value to decide
   whether to return a shortened form of the response URL.  If the AS
   cannot shorten its response URL enough to fit in the requested size,
   the AS SHOULD return an error. [[ Editor's note: Or maybe just ignore
   this part of the interaction request? ]]

   The means by which the client will activate this URL is out of scope
   of this specification, but common methods include an HTTP redirect,
   launching a browser on the user's device, providing a scannable image
   encoding, and printing out a URL to an interactive console for the
   user to copy and paste into a browser.

   "interact": {
      "redirect": 255
   }

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

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2.5.2.  Open an Application-specific URL

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

   "interact": {
      "app": true
   }

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

   [[ Editor's note: this is similar to the "redirect" above today as
   most apps use captured URLs, but there seems to be a desire for
   splitting the web-based interaction and app-based interaction into
   different URIs.  There's also the possibility of wanting more in the
   payload than can be reasonably put into the URL, or at least having
   separate payloads. ]]

2.5.3.  Receive a Callback After Interaction

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

   uri  REQUIRED.  Indicates the URI to send the RO to after
      interaction.  This URI MAY be unique per request and MUST be
      hosted by or accessible by the RC.  This URI MUST NOT contain any
      fragment component.  This URI MUST be protected by HTTPS, be
      hosted on a server local to the 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 restricted by the AS based on the RC's
      presented key information.  The callback URI SHOULD be presented
      to the RO during the interaction phase before redirect.

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

   method  REQUIRED.  The callback method that the AS will use to

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      contact the client.  Valid values include "redirect"
      Section 2.5.3.1 and "push" Section 2.5.3.2, with other values
      defined by a registry TBD (Section 12).

   hash_method  OPTIONAL.  The hash calculation mechanism to be used for
      the callback hash in Section 4.4.3.  Can be one of sha3 or sha2.
      If absent, the default value is "sha3".  [[ Editor's note: This
      should be expandable via a registry of cryptographic options, and
      it would be good if we didn't define our own identifiers here.
      See also note about cryptographic functions in Section 4.4.3.  ]]

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

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

   Note that the means by which the user arrives at the AS is declared
   separately from the user's return using this callback mechanism.

2.5.3.1.  Receive an HTTP Callback Through the Browser

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

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

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

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   Since the incoming request to the callback URL is from the user's
   browser, the client MUST require the user to be present on the
   connection.

2.5.3.2.  Receive an HTTP Direct Callback

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

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

   Requests to the pushback URI MUST be processed as described in
   Section 4.4.2.

   Since the incoming request to the pushback URL is from the AS and not
   from the user's browser, the client MUST NOT require the user to be
   present.

2.5.4.  Display a Short User Code

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

   "interact": {
       "user_code": true
   }

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

2.5.5.  Extending Interaction Capabilities

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

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   [[ Editor's note: we should have guidance in here about how to define
   other interaction capabilities.  There's already interest in defining
   message-based protocols and challenge-response protocols, for
   example. ]]

2.6.  Providing Displayable Client Information

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

   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"
       }

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

   The AS SHOULD use these values during interaction with the user.  The
   AS MAY restrict display values to specific clients, as identified by
   their keys in Section 2.3.

   [[ Editor's note: this might make sense to combine with the "key"
   field, but some classes of more dynamic client vary those fields
   separately from the key material.  We should also consider things
   like signed statements for client attestation, but that might fit
   better into a different top-level field instead of this "display"
   field. ]]

2.7.  Declaring Client Capabilities

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

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

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2.8.  Referencing an Existing Grant Request

   If the client has a reference handle from a previously granted
   request, it MAY send that reference in the "reference" field.  This
   field is a single string.

   "existing_grant": "80UPRY5NM33OMUKMKSKU"

   The AS MUST dereference the grant associated with the reference and
   process this request in the context of the referenced one.

   [[ Editor's note: this basic capability is to allow for both step-up
   authorization and downscoped authorization, but by explicitly
   creating a new request and not modifying an existing one.  What's the
   best guidance for how an AS should process this? ]]

2.9.  Requesting OpenID Connect Claims

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

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

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

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

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   [[ Editor's note: I'm not a fan of GNAP defining how OIDC would work
   and would rather that work be done by the OIDF.  However, I think it
   is important for discussion to see this kind of thing in context with
   the rest of the protocol, for now. ]]

2.10.  Extending The Grant Request

   The request object MAY be extended by registering new items in a
   registry TBD (Section 12).  Extensions SHOULD be orthogonal to other
   parameters.  Extensions MUST document any aspects where the

   [[ Editor's note: we should have more guidance and examples on what
   possible top-level extensions would look like.  Things like an OIDC
   "claims" request or a VC query, for example. ]]

3.  Grant Response

   In response to a client's request, the AS responds with a JSON object
   as the HTTP entity body.

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

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

   In this example, the AS is returning an access token (Section 3.2.1),
   a continuation handle (Section 3.1), and a subject identifier
   (Section 3.4).

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{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue"
    },
    "subject": {
        "sub_ids": [ {
           "subject_type": "email",
           "email": "user@example.com",
        } ]
    }
}

3.1.  Request Continuation Handle

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

   handle  REQUIRED.  A unique reference for the grant request.

   uri  REQUIRED.  The URI at which the client can make continuation
      requests.  This URI MAY vary per client or ongoing request, or MAY
      be stable at the AS.

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

   expires_in  OPTIONAL.  The number of seconds in which the handle will
      expire.  The client MUST NOT use the handle past this time.  The
      handle MAY be revoked at any point prior to its expiration.

   {
       "continue": {
           "handle": "80UPRY5NM33OMUKMKSKU",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

   The client can use the values of this field as described in
   Section 5.

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

3.2.  Access Tokens

   If the AS has successfully granted one or more access tokens, it
   responds with one of these fields.  The AS MUST NOT respond with both
   fields.

   [[ Editor's note: I really don't like the dichotomy between
   "access_token" and "multiple_access_tokens" and their being mutually
   exclusive, and I think we should design away from this pattern toward
   something less error-prone. ]]

3.2.1.  Single Access Token

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

   value  REQUIRED.  The value of the access token as a string.  The
      value is opaque to the client.  The value SHOULD be limited to
      ASCII characters to facilitate transmission over HTTP headers and
      elements without additional encoding.

   proof  REQUIRED.  The proofing presentation mechanism used for
      presenting this access token to an RS.  See the section on using
      access tokens (Section 7) for details on possible values to this
      field and their requirements.

   manage  OPTIONAL.  The management URI for this access token.  If
      provided, the client MAY manage its access token as described in
      managing an access token lifecycle (Section 6).  This URI MUST NOT
      include the access token value and MAY be different for each
      access token.

   resources  OPTIONAL.  A description of the rights associated with
      this access token, as defined in requesting resource access
      (Section 3.2.1).  If included, this MUST reflect the rights
      associated with the issued access token.  These rights MAY vary
      from what was requested by the client.

   expires_in  OPTIONAL.  The number of seconds in which the access will
      expire.  The client MUST NOT use the access token past this time.
      The access token MAY be revoked at any point prior to its
      expiration.

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   key  The key that the token is bound to, REQUIRED if the token is
      sender-constrained.  The key MUST be in a format described in
      Section 2.3. [[ Editor's note: this isn't quite right, since the
      request section includes a "proof" field that we already have
      here.  A possible solution would be to only have a "key" field as
      defined above and its absence indicates a bearer token? ]]

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

3.2.2.  Multiple Access Tokens

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

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

   Each access token corresponds to the named resources arrays in the
   client's request.  The AS MAY not issue one or more of the requested
   access tokens.  In such cases all of the issued access tokens are
   included without the omitted token.  The multiple access token
   response MUST be used when multiple access tokens are requested, even
   if only one access token is issued.

   If the client requested a single access token (Section 2.1.1), the AS
   MUST NOT respond with multiple access tokens.

   Each access token MAY have different proofing mechanisms.  If used,
   each access token MUST have different management URIs.

3.3.  Interaction Capabilities

   If the client has indicated a capability to interact with the user in
   its request (Section 2.5), and the AS has determined that interaction
   is both supported and necessary, the AS responds to the client with
   any of the following values in the "interact" field of the response.
   There is no preference order for interaction capabilities in the
   response, and it is up to the client to determine which ones to use.

   The AS MUST NOT respond with any interaction capability that the
   client did not indicate in its request.

3.3.1.  Redirection to an arbitrary URL

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

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

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

3.3.2.  Launch of an application URL

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

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

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

   [[ Editor's note: This will probably need to be expanded to an object
   to account for other parameters needed in app2app use cases, like
   addresses for distributed storage systems, server keys, and the like.
   Details TBD as people build this out. ]]

3.3.3.  Callback to a Client URL

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

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

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

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

3.3.4.  Display of a Short User Code

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

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

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

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

   The client MUST communicate the "code" to the user in some fashion,
   such as displaying it on a screen or reading it out audibly.  The
   client SHOULD also communicate the URL if possible.

   The "code" is a one-time-use credential that the AS uses to identify
   the pending request from the RC.  When the user enters this code into
   the AS, the AS MUST determine the pending request that it was
   associated with.  If the AS does not recognize the entered code, the
   AS MUST display an error to the user.

   As this interaction capability is designed to facilitate interaction
   via a secondary device, it is not expected that the client redirect
   the user to the URL given here at runtime.  Consequently, the URL
   needs to be stable enough that a client could be statically
   configured with it, perhaps referring the user to the URL via

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   documentation instead of through an interactive means.  If the client
   is capable of communicating an arbitrary URL to the user, such as
   through a scannable code, the client can use the "redirect"
   (Section 2.5.1) capability for this purpose.

3.3.5.  Extending Interaction Capability Responses

   Extensions to this specification can define new interaction
   capability responses in a registry TBD (Section 12).

3.4.  Returning User Information

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

   sub_ids  An array of subject identifiers for the user, as defined by
      [I-D.ietf-secevent-subject-identifiers]. [[ Editor's note: privacy
      considerations are needed around returning identifiers. ]]

   assertions  An object containing assertions as values keyed on the
      assertion type defined by a registry TBD (Section 12).  [[
      Editor's note: should this be an array of objects with internal
      typing like the sub_ids?  Do we expect more than one assertion per
      user anyway? ]]

   updated_at  Timestamp in integer seconds indicating when the
      identified account was last updated.  The client MAY use this
      value to determine if it needs to request updated profile
      information through an identity API.

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

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

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3.5.  Returning Dynamically-bound Reference Handles

   Many parts of the client's request can be passed as either a value or
   a reference.  Some of these references, such as for the client's keys
   or the resources, can sometimes be managed statically through an
   admin console or developer portal provided by the AS or RS.  If
   desired, the AS MAY also generate and return some of these references
   dynamically to the client in its response to facilitate multiple
   interactions with the same software.  The client SHOULD use these
   references in future requests in lieu of sending the associated data
   value.  These handles are intended to be used on future requests.

   Dynamically generated handles are string values that MUST be
   protected by the client as secrets.  Handle values MUST be
   unguessable and MUST NOT contain any sensitive information.  Handle
   values are opaque to the client. [[ Editor's note: these used to be
   objects to allow for expansion to future elements, like a management
   URI or different presentation types or expiration, but those weren't
   used in practice.  Is that desirable anymore or is collapsing them
   like this the right direction? ]]

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

   key_handle  A value used to represent the information in the key
      object that the client can use in a future request, as described
      in Section 2.3.2.

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

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

   {
       "user_handle": "XUT2MFM1XBIKJKSDU8QM",
       "key_handle": "7C7C4AZ9KHRS6X63AJAO",
       "access_token": {
           "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
           "proof": "bearer"
       }
   }

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3.6.  Error response

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

   error  The error code.

   {

     "error": "user_denied"

   }

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

   user_denied  The RO denied the request.

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

   unknown_handle  The request referenced an unknown handle.

   [[ Editor's note: I think we will need a more robust error mechanism,
   and we need to be more clear about what error states are allowed in
   what circumstances.  Additionally, is the "error" parameter exclusive
   with others in the return? ]]

3.7.  Extending the Response

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

   [[ Editor's note: what guidance should we give to designers on this?
   ]]

4.  Interaction at the AS

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

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

   *  authenticate the user as RO

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

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

   [[ Editor's note: there are some privacy and security considerations
   here but for the most part we don't want to be overly prescriptive
   about the UX, I think. ]]

4.1.  Interaction at a Redirected URI

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

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

4.2.  Interaction at the User Code URI

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

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

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4.3.  Interaction through an Application URI

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

   [[ Editor's note: Should we have anything to say about an app sending
   information to a back-end to get details on the pending request? ]]

4.4.  Post-Interaction Completion

   Upon completing an interaction with the user, if a "callback"
   (Section 3.3.3) capability is available with the current request, the
   AS MUST follow the appropriate method at the end of interaction to
   allow the client to continue.  If neither capability is available,
   the AS SHOULD instruct the user to return to their client software
   upon completion.  Note that these steps still take place in most
   error cases, such as when the user has denied access.  This allows
   the client to potentially recover from the error state without
   restarting.

   [[ Editor's note: there might be some other kind of push-based
   notification or callback that the client can use, or an out-of-band
   non-HTTP protocol.  The AS would know about this if supported and
   used, but the guidance here should be written in such a way as to not
   be too restrictive in the next steps that it can take.  Still, it's
   important that the AS not expect or even allow clients to poll if the
   client has stated it can take a callback of some form, otherwise that
   sets up a potential session fixation attack vector that the client is
   trying to and able to avoid. ]]

   The AS MUST calculate a hash value as described in Section 4.4.3.
   The client will use this value to validate the return call from the
   AS.

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

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

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4.4.1.  Completing Interaction with a Callback URI

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

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

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

   interact_ref  REQUIRED.  The interaction reference generated for this
      interaction.

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

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

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

4.4.2.  Completing Interaction with a Pushback URI

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

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

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

   interact_ref  REQUIRED.  The interaction reference generated for this
      interaction.

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

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

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

4.4.3.  Calculating the interaction hash

   The "hash" parameter in the request to the client's callback URL ties
   the front channel response to an ongoing request by using values
   known only to the parties involved.  This prevents several kinds of
   session fixation attacks against the client.

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

   VJLO6A4CAYLBXHTR0KRO
   MBDOFXG4Y5CVJCX821LH
   4IFWWIKYBC2PQ6U56NL1

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

   [[ Editor's note: these hash algorithms should be pluggable, and
   ideally we shouldn't redefine yet another crypto registry for this
   purpose, but I'm not convinced an appropriate one already exists.
   Furthermore, we should be following best practices here whether it's
   a plain hash, a keyed MAC, an HMAC, or some other form of
   cryptographic function.  I'm not sure what the defaults and options
   ought to be, but SHA512 and SHA3 were picked based on what was
   available to early developers. ]]

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4.4.3.1.  SHA3

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

p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A

4.4.3.2.  SHA2

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

62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bpj84rh4mC9aE9x7HPBFcIHw

5.  Continuing a Grant Request

   If the client receives a continuation element in its response
   Section 3.1, the client can make an HTTP POST call to the
   continuation URI with a JSON object.  The client MUST send the handle
   reference from the continuation element in its request as a top-level
   JSON parameter.

   {
     "handle": "tghji76ytghj9876tghjko987yh"
   }

   The client MAY include other parameters as described here or as
   defined a registry TBD (Section 12).

   [[ Editor's note: We probably want to allow other parameters, like
   modifying the resources requested or providing more user information.
   We'll certainly have some kinds of specific challenge-response
   protocols as there's already been interest in that kind of thing, and
   the continuation request is the place where that would fit. ]]

   If a "wait" parameter was included in the continuation response, the
   client MUST NOT call the continuation URI prior to waiting the number
   of seconds indicated.  If no "wait" period is indicated, the client
   SHOULD wait at least 5 seconds [[ Editor's note: what's a reasonable
   amount of time so as not to DOS the server?? ]].

   The response from the AS is a JSON object and MAY contain any of the
   elements described in Section 3, with some variations:

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   If the AS determines that the client can make a further continuation
   request, the AS MUST include a new "continue" response element
   (Section 3.1).  The returned handle value MUST NOT be the same as
   that used to make the continuation request, and the continuation URI
   MAY remain the same.  If the AS does not return a new "continue"
   response element, the client MUST NOT make an additional continuation
   request.  If a client does so, the AS MUST return an error.

   If the AS determines that the client still needs to drive interaction
   with the user, the AS MAY return appropriate responses for any of the
   interaction mechanisms (Section 3.3) the client indicated in its
   initial request (Section 2.5).  Unique values such as interaction
   URIs and nonces SHOULD be re-generated and not re-used.

   The client MUST present proof of the same key identified in the
   initial request (Section 2.3) by signing the request as described in
   Section 8.  This requirement is in place whether or not the AS had
   previously registered the client's key as described in Section 2.3.1.

5.1.  Continuing after a Finalized Interaction

   If the client has received an interaction reference from a "callback"
   (Section 4.4.1) message, the client MUST include the
   "interaction_ref" in its continuation request.  The client MUST
   validate the hash before making the continuation request, but note
   that the client does not send the hash back to the AS in the request.

   {
     "handle": "tghji76ytghj9876tghjko987yh",
     "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

5.2.  Continuing after Tokens are Issued

   A request MAY be continued even after access tokens have been issued,
   so long as the handle is valid.  The AS MAY respond to such a
   continuation request with new access tokens as described in
   Section 3.2 based on the client's original request.  The AS SHOULD
   revoke existing access tokens.  If the AS determines that the client
   can make a further continuation request in the future, the AS MUST
   include a new "continue" response element (Section 3.1).  The
   returned handle value MUST NOT be the same as that used to make the
   continuation request, and the continuation URI MAY remain the same.
   If the AS does not return a new "continue" response element, the
   client MUST NOT make an additional continuation request.  If a client
   does so, the AS MUST return an error.

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6.  Token Management

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

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

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

   If the token is a bearer token, the client MUST present proof of the
   same key identified in the initial request (Section 2.3) as described
   in Section 8.

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

6.1.  Rotating the Access Token

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

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

   The AS validates that the token presented is associated with the
   management URL, that the AS issued the token to the given client, and
   that the presented key is appropriate to the token.  The access token
   MAY be expired, and in such cases the AS SHOULD honor the rotation
   request to the token management URL.  The AS MAY store different
   lifetimes for the use of the token in rotation vs. its use at an RS.

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   If the token is validated and the key is appropriate for the request,
   the AS will invalidate the current access token associated with this
   URL, if possible, and return a new access token response as described
   in Section 3.2.1.  The value of the access token MUST NOT be the same
   as the current value of the access token used to access the
   management API.  The response MAY include an updated access token
   management URL as well, and if so, the client MUST use this new URL
   to manage the new access token.

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

6.2.  Revoking the Access Token

   The client makes an HTTP DELETE request to the token management URI,
   signing the request with its key.

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

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   If the token was issued to the client identified by the key, the AS
   will invalidate the current access token associated with this URL, if
   possible, and return an HTTP 204 response code.

   204 No Content

7.  Using Access Tokens

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

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

   Authorization: Bearer OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0

   If the "proof" value is any other string, the access token is sent
   using the HTTP authorization scheme "GNAP" along with a key proof as
   described in Section 8 for the key bound to the access token.  For
   example, a "jwsd"-bound access token is sent as follows:

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

   [[ Editor's note: I don't actually like the idea of using only one
   header type for differently-bound access tokens, but instead these
   values should somehow reflect the key binding types.  Maybe there can
   be multiple fields after the "GNAP" keyword using structured headers?
   Or a set of derived headers like GNAP-mtls?  This might also be
   better as a separate specification, like OAuth 2. ]]

8.  Binding Keys

   Any keys presented by the RC to the AS or RS MUST be validated as
   part of the request in which they are presented.  The type of binding
   used is indicated by the proof parameter of the key section in the
   initial request Section 2.3.  Values defined by this specification
   are as follows:

   jwsd  A detached JWS signature header

   jws  Attached JWS payload

   mtls  Mutual TLS certificate verification

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

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   httpsig  HTTP Signing signature header

   oauthpop  OAuth PoP key proof authentication header

   Additional values can be defined by a registry TBD (Section 12).

   The keys presented by the RC in the Section 2 MUST be proved in all
   continuation requests Section 5 and token management requests
   Section 6.  The AS MUST validate all keys presented by the RC
   (Section 2.3) or referenced in an ongoing transaction at each call.

8.1.  Detached JWS

   This method is indicated by "jwsd" in the "proof" field.  To sign a
   request, 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 for this request.  The JWS
   header MUST contain an alg field appropriate for the key identified
   by kid and MUST NOT be none.

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

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

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

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

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   [[ Editor's note: this is a potentially fragile signature mechanism.
   It doesn't protect the method or URL of the request in the signature,
   but it's simple to calculate and useful for body-driven requests,
   like the client to the AS.  We might want to remove this in favor of
   general-purpose HTTP signing. ]]

8.2.  Attached JWS

   This method is indicated by "jws" in the "proof" field.  To sign a
   request, the RC takes the serialized body of the request JSON and
   signs it using JWS [RFC7515].  The header of the JWS MUST contain the
   kid field of the key bound to this RC during this request.  The JWS
   header MUST contain an alg field appropriate for the key identified
   by kid and MUST NOT be none.

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

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

   eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.ewogICAgIm
   NsaWVudCI6IHsKICAgICAgICAibmFtZSI6ICJNeSBDbGllbnQgRGlzcGxheSBOYW1l
   IiwKICAgICAgICAidXJpIjogImh0dHBzOi8vZXhhbXBsZS5uZXQvY2xpZW50IgogIC
   AgfSwKICAgICJyZXNvdXJjZXMiOiBbCiAgICAgICAgImRvbHBoaW4tbWV0YWRhdGEi
   CiAgICBdLAogICAgImludGVyYWN0IjogewogICAgICAgICJyZWRpcmVjdCI6IHRydW
   UsCiAgICAgICAgImNhbGxiYWNrIjogewogICAgCQkidXJpIjogImh0dHBzOi8vY2xp
   ZW50LmZvbyIsCiAgICAJCSJub25jZSI6ICJWSkxPNkE0Q0FZTEJYSFRSMEtSTyIKIC
   AgIAl9CiAgICB9LAogICAgImtleXMiOiB7CgkJInByb29mIjogImp3c2QiLAogICAg
   ICAgICJqd2tzIjogewogICAgICAgICAgICAia2V5cyI6IFsKICAgICAgICAgICAgIC
   AgIHsKICAgICAgICAgICAgICAgICAgICAia3R5IjogIlJTQSIsCiAgICAgICAgICAg
   ICAgICAgICAgImUiOiAiQVFBQiIsCiAgICAgICAgICAgICAgICAgICAgImtpZCI6IC
   J4eXotMSIsCiAgICAgICAgICAgICAgICAgICAgImFsZyI6ICJSUzI1NiIsCiAgICAg
   ICAgICAgICAgICAgICAgIm4iOiAia09CNXJSNEp2MEdNZUxhWTZfSXRfcjNPUndkZj
   hjaV9KdGZmWHlhU3g4eFlKQ0NOYU9LTkpuX096MFloZEhiWFRlV081QW95c3BEV0pi
   TjV3XzdiZFdEeGdwRC15NmpuRDF1OVloQk9DV09iTlBGdnBrVE04TEM3U2RYR1JLeD
   JrOE1lMnJfR3NzWWx5UnBxdnBCbFk1LWVqQ3l3S1JCZmN0UmNuaFRUR056dGJiREJV
   eURTV21GTVZDSGU1bVhUNGNMMEJ3clpDNlMtdXUtTEF4MDZhS3dRT1B3WU9HT3NsSz
   hXUG0xeUdka2FBMXVGX0ZwUzZMUzYzV1lQSGlfQXAyQjdfOFdidzR0dHpiTVNfZG9K
   dnVEYWdXOEExSXAzZlhGQUh0UkFjS3c3cmRJNF9YbG42NmhKeEZla3BkZldkaVBRZG
   RRNlkxY0syVTNvYnZVZzd3IgogICAgICAgICAgICAgICAgfQogICAgICAgICAgICBd
   CiAgICAgICAgfQogICAgfQp9.Y287HMtaY0EegEjoTd_04a4GC6qV48GgVbGKOhHdJ
   nDtD0VuUlVjLfwne8AuUY3U7e89zUWwXLnAYK_BiS84M8EsrFvmv8yDLWzqveeIpcN
   5_ysveQnYt9Dqi32w6IOtAywkNUDZeJEdc3z5s9Ei8qrYFN2fxcu28YS4e8e_cHTK5
   7003WJu-wFn2TJUmAbHuqvUsyTb-nzYOKxuCKlqQItJF7E-cwSb_xULu-3f77BEU_v
   GbNYo5ZBa2B7UHO-kWNMSgbW2yeNNLbLC18Kv80GF22Y7SbZt0e2TwnR2Aa2zksuUb
   ntQ5c7a1-gxtnXzuIKa34OekrnyqE1hmVWpeQ

   [[ Editor's note: A downside to this method is that it requires the
   content type to be something other than application/json, and it
   doesn't work against an RS without additional profiling since it
   requires things to be sent in the body.  Additionally it is
   potentially fragile like a detached JWS since a multi-tier system
   could parse the payload and pass the parsed payload downstream with
   potential transformations.  Furthermore, it doesn't protect the
   method or URL of the request in the signature.  We might want to
   remove this in favor of general-purpose HTTP signing. ]]

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8.3.  Mutual TLS

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

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

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

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            "nonce": "VJLO6A4CAYLBXHTR0KRO"
        }
    },
    "key": {
        "proof": "mtls",
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3
MDUGA1UEAwwuQmVzcG9rZSBFbmdpbmVlcmluZyBSb290IENlcnRpZmljYXRlIEF1d
Ghvcml0eTELMAkGA1UECAwCTUExCzAJBgNVBAYTAlVTMRkwFwYJKoZIhvcNAQkBFg
pjYUBic3BrLmlvMRwwGgYDVQQKDBNCZXNwb2tlIEVuZ2luZWVyaW5nMQwwCgYDVQQ
LDANNVEkwHhcNMTkwNDEwMjE0MDI5WhcNMjQwNDA4MjE0MDI5WjB8MRIwEAYDVQQD
DAlsb2NhbGhvc3QxCzAJBgNVBAgMAk1BMQswCQYDVQQGEwJVUzEgMB4GCSqGSIb3D
QEJARYRdGxzY2xpZW50QGJzcGsuaW8xHDAaBgNVBAoME0Jlc3Bva2UgRW5naW5lZX
JpbmcxDDAKBgNVBAsMA01USTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggE
BAMmaXQHbs/wc1RpsQ6Orzf6rN+q2ijaZbQxD8oi+XaaN0P/gnE13JqQduvdq77Om
J4bQLokqsd0BexnI07Njsl8nkDDYpe8rNve5TjyUDCfbwgS7U1CluYenXmNQbaYND
OmCdHwwUjV4kKREg6DGAx22Oq7+VHPTeeFgyw4kQgWRSfDENWY3KUXJlb/vKR6lQ+
aOJytkvj8kVZQtWupPbvwoJe0na/ISNAOhL74w20DWWoDKoNltXsEtflNljVoi5nq
smZQcjfjt6LO0T7O1OX3Cwu2xWx8KZ3n/2ocuRqKEJHqUGfeDtuQNt6Jz79v/OTr8
puLWaD+uyk6NbtGjoQsCAwEAAaOBiTCBhjAJBgNVHRMEAjAAMAsGA1UdDwQEAwIF4
DBsBgNVHREEZTBjgglsb2NhbGhvc3SCD3Rsc2NsaWVudC5sb2NhbIcEwKgBBIERdG
xzY2xpZW50QGJzcGsuaW+GF2h0dHA6Ly90bHNjbGllbnQubG9jYWwvhhNzc2g6dGx
zY2xpZW50LmxvY2FsMA0GCSqGSIb3DQEBCwUAA4IBAQCKKv8WlLrT4Z5NazaUrYtl
TF+2v0tvZBQ7qzJQjlOqAcvxry/d2zyhiRCRS/v318YCJBEv4Iq2W3I3JMMyAYEe2
573HzT7rH3xQP12yZyRQnetdiVM1Z1KaXwfrPDLs72hUeELtxIcfZ0M085jLboXhu
fHI6kqm3NCyCCTihe2ck5RmCc5l2KBO/vAHF0ihhFOOOby1v6qbPHQcxAU6rEb907
/p6BW/LV1NCgYB1QtFSfGxowqb9FRIMD2kvMSmO0EMxgwZ6k6spa+jk0IsI3klwLW
9b+Tfn/daUbIDctxeJneq2anQyU2znBgQl6KILDSF4eaOqlBut/KNZHHazJh"
    }
}

8.4.  DPoP

   This method is indicated by "dpop" in the "proof" field.  The RC
   creates a Demonstration of Proof-of-Possession signature header as
   described in [I-D.ietf-oauth-dpop] section 2.

 POST /transaction HTTP/1.1
 Host: server.example.com
 Content-Type: application/json
 DPoP: eyJ0eXAiOiJkcG9wK2p3dCIsImFsZyI6IlJTMjU2IiwiandrIjp7Imt0eSI6Il
 JTQSIsImUiOiJBUUFCIiwia2lkIjoieHl6LWNsaWVudCIsImFsZyI6IlJTMjU2Iiwibi
 I6Inp3Q1RfM2J4LWdsYmJIcmhlWXBZcFJXaVk5SS1uRWFNUnBablJySWpDczZiX2VteV
 RrQmtEREVqU3lzaTM4T0M3M2hqMS1XZ3hjUGRLTkdaeUlvSDNRWmVuMU1LeXloUXBMSk
 cxLW9MTkxxbTdwWFh0ZFl6U2RDOU8zLW9peXk4eWtPNFlVeU5aclJSZlBjaWhkUUNiT1
 9PQzhRdWdtZzlyZ05ET1NxcHBkYU5lYXMxb3Y5UHhZdnhxcnoxLThIYTdna0QwMFlFQ1
 hIYUIwNXVNYVVhZEhxLU9fV0l2WVhpY2c2STVqNlM0NFZOVTY1VkJ3dS1BbHluVHhRZE
 1BV1AzYll4VlZ5NnAzLTdlVEpva3ZqWVRGcWdEVkRaOGxVWGJyNXlDVG5SaG5oSmd2Zj
 NWakRfbWFsTmU4LXRPcUs1T1NEbEhUeTZnRDlOcWRHQ20tUG0zUSJ9fQ.eyJodHRwX21

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 ldGhvZCI6IlBPU1QiLCJodHRwX3VyaSI6Imh0dHA6XC9cL2hvc3QuZG9ja2VyLmludGV
 ybmFsOjk4MzRcL2FwaVwvYXNcL3RyYW5zYWN0aW9uIiwiaWF0IjoxNTcyNjQyNjEzLCJ
 qdGkiOiJIam9IcmpnbTJ5QjR4N2pBNXl5RyJ9.aUhftvfw2NoW3M7durkopReTvONng1
 fOzbWjAlKNSLL0qIwDgfG39XUyNvwQ23OBIwe6IuvTQ2UBBPklPAfJhDTKd8KHEAfidN
 B-LzUOzhDetLg30yLFzIpcEBMLCjb0TEsmXadvxuNkEzFRL-Q-QCg0AXSF1h57eAqZV8
 SYF4CQK9OUV6fIWwxLDd3cVTx83MgyCNnvFlG_HDyim1Xx-rxV4ePd1vgDeRubFb6QWj
 iKEO7vj1APv32dsux67gZYiUpjm0wEZprjlG0a07R984KLeK1XPjXgViEwEdlirUmpVy
 T9tyEYqGrTfm5uautELgMls9sgSyE929woZ59elg

 {
     "client": {
         "name": "My Client Display Name",
         "uri": "https://example.net/client"
     },
     "resources": [
         "dolphin-metadata"
     ],
     "interact": {
         "redirect": true,
         "callback": {
             "method": "redirect",
             "uri": "https://client.foo",
             "nonce": "VJLO6A4CAYLBXHTR0KRO"
         }
     },
     "key": {
         "proof": "dpop",
         "jwk": {
                     "kty": "RSA",
                     "e": "AQAB",
                     "kid": "xyz-1",
                     "alg": "RS256",
                     "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_JtffXyaSx8xYJ
 CCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-y6jnD1u9YhBOCWObNPFvpkTM
 8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCH
 e5mXT4cL0BwrZC6S-uu-LAx06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2
 B7_8Wbw4ttzbMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6Y
 1cK2U3obvUg7w"
         }
     }
 }

   [[ Editor's note: this method requires duplication of the key in the
   header and the request body, which is redundant and potentially
   awkward.  The signature also doesn't protect the body of the request.
   ]]

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8.5.  HTTP Signing

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

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

   {
       "client": {
           "name": "My Client Display Name",
           "uri": "https://example.net/client"
       },
       "resources": [
           "dolphin-metadata"
       ],
       "interact": {
           "redirect": true,
           "callback": {
               "method": "push",
               "uri": "https://client.foo",
               "nonce": "VJLO6A4CAYLBXHTR0KRO"
           }
       },
       "key": {
           "proof": "httpsig",
           "jwk": {
                       "kty": "RSA",
                       "e": "AQAB",
                       "kid": "xyz-1",
                       "alg": "RS256",
                       "n": "kOB5rR4Jv0GMeLaY6_It_r3ORwdf8ci_J
   tffXyaSx8xYJCCNaOKNJn_Oz0YhdHbXTeWO5AoyspDWJbN5w_7bdWDxgpD-
   y6jnD1u9YhBOCWObNPFvpkTM8LC7SdXGRKx2k8Me2r_GssYlyRpqvpBlY5-

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   ejCywKRBfctRcnhTTGNztbbDBUyDSWmFMVCHe5mXT4cL0BwrZC6S-uu-LAx
   06aKwQOPwYOGOslK8WPm1yGdkaA1uF_FpS6LS63WYPHi_Ap2B7_8Wbw4ttz
   bMS_doJvuDagW8A1Ip3fXFAHtRAcKw7rdI4_Xln66hJxFekpdfWdiPQddQ6
   Y1cK2U3obvUg7w"
           }
       }
   }

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

8.6.  OAuth PoP

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

   *  The at (access token) field MUST be [note: this is in contrast to
      the requirements in the existing spec] unless this method is being
      used in conjunction with an access token as in Section 7.

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

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

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   G0J4bPVnTI5St9hJYvvh7FE8JirIg

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

9.  Discovery

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

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

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

   capabilities  OPTIONAL.  A list of the AS's capabilities.  The values
      of this result MAY be used by the RC in the capabilities section
      (Section 2.7) of the request.

   interaction_methods  OPTIONAL.  A list of the AS's interaction
      methods.  The values of this list correspond to the possible
      fields in the interaction section (Section 2.5) of the request.

   key_proofs  OPTIONAL.  A list of the AS's supported key proofing
      mechanisms.  The values of this list correspond to possible values
      of the "proof" field of the key section (Section 2.3) of the
      request.

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

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

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

10.  Resource Servers

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

   [[ Editor's note: This section is for discussion of possible advanced
   functionality.  It seems like it should be a separate document or set
   of documents, and it's not even close to being well-baked.  This also
   adds additional endpoints to the AS, as this is separate from the

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   token request process, and therefore would require RS-facing
   discovery or configuration information to make it work.  Also-also,
   it does presume the RS can sign requests in the same way that a
   client does, but hopefully we can be more consistent with this than
   RFC7662 was able to do. ]]

10.1.  Introspecting a Token

   When the RS receives an access token, it can call the introspection
   endpoint at the AS to get token information. [[ Editor's note: this
   isn't super different from the token management URIs, but the RS has
   no way to get that URI, and it's bound to different keys. ]]

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

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

   {
       "access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
   }

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

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   Content-type: application/json

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

10.2.  Deriving a downstream token

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

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

   [[ Editor's note: this is similar to but based on the access token
   and not the grant.  The fact that the keys presented are not the ones
   used for the access token should indicate that it's a different party
   and a different kind of request. ]]

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

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

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

10.3.  Registering a Resource Handle

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

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

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

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

   }

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

   Content-type: application/json

   {
       "resource_handle": "FWWIKYBQ6U56NL1"
   }

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

   [[ Editor's note: It's not an exact match here because the
   "resource_handle" returned now represents a collection of objects
   instead of a single one.  Perhaps we should let this return a list of
   strings instead?  Or use a different syntax than the resource
   request?  Also, this borrows heavily from UMA 2's "distributed
   authorization" model and, like UMA, might be better suited to an
   extension than the core protocol. ]]

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10.4.  Requesting a Resources With Insufficient Access

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

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

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

   [[ Editor's note: this borrows heavily from UMA 2's "distributed
   authorization" model and, like UMA, might be better suited to an
   extension than the core protocol. ]]

11.  Acknowledgements

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

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

12.  IANA Considerations

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

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13.  Security Considerations

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

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

14.  Privacy Considerations

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

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

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

15.  Normative References

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

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

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

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

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   [I-D.ietf-secevent-subject-identifiers]
              Backman, A. and M. Scurtescu, "Subject Identifiers for
              Security Event Tokens", Work in Progress, Internet-Draft,
              draft-ietf-secevent-subject-identifiers-05, 24 July 2019,
              <http://www.ietf.org/internet-drafts/draft-ietf-secevent-
              subject-identifiers-05.txt>.

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

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

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

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

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

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

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

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

   [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>.

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   [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>.

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

Appendix A.  Document History

   *  -10

      -  Switched to xml2rfc v3 and markdown source.

      -  Updated based on Design Team feedback and reviews.

      -  Added acknowledgements list.

      -  Added sequence diagrams and explanations.

      -  Collapsed "short_redirect" into regular redirect request.

      -  Separated pass-by-reference into subsections.

      -  Collapsed "callback" and "pushback" into a single mode-switched
         method.

      -  Add OIDC Claims request object example.

   *  -09

      -  Major document refactoring based on request and response
         capabilities.

      -  Changed from "claims" language to "subject identifier"
         language.

      -  Added "pushback" interaction capability.

      -  Removed DIDCOMM interaction (better left to extensions).

      -  Excised "transaction" language in favor of "Grant" where
         appropriate.

      -  Added token management URLs.

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      -  Added separate continuation URL to use continuation handle
         with.

      -  Added RS-focused functionality section.

      -  Added notion of extending a grant request based on a previous
         grant.

      -  Simplified returned handle structures.

   *  -08

      -  Added attached JWS signature method.

      -  Added discovery methods.

   *  -07

      -  Marked sections as being controlled by a future registry TBD.

   *  -06

      -  Added multiple resource requests and multiple access token
         response.

   *  -05

      -  Added "claims" request and response for identity support.

      -  Added "capabilities" request for inline discovery support.

   *  -04

      -  Added crypto agility for callback return hash.

      -  Changed "interaction_handle" to "interaction_ref".

   *  -03

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

      -  Created signed return parameter for front channel return.

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

      -  Changed "key" to "keys".

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      -  Separated key proofing from key presentation.

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

   *  -02

      -  Minor editorial cleanups.

   *  -01

      -  Made JSON multimodal for handle requests.

      -  Major updates to normative language and references throughout
         document.

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

   *  -00

      -  Initial submission.

Appendix B.  Component Data Models

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

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

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

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

Appendix C.  Example Protocol Flows

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

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

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C.1.  Redirect-Based User Interaction

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

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

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

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

   The AS processes the request and determines that the RO needs to
   interact.  The AS returns the following response giving the client
   the information it needs to connect.  The AS has also indicated to
   the client that it can use the given key handle to identify itself in
   future calls.

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Content-type: application/json

{
    "interact": {
       "redirect": "https://server.example.com/interact/4CF492MLVMSW9MKMXKHQ",
       "callback": "MBDOFXG4Y5CVJCX821LH"
    }
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue"
    },
    "key_handle": "7C7C4AZ9KHRS6X63AJAO"
}

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

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

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

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

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

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

   {
       "handle": "80UPRY5NM33OMUKMKSKU",
       "interact_ref": "4IFWWIKYBC2PQ6U56NL1"
   }

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

Content-type: application/json

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

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C.2.  Secondary Device Interaction

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

   The client initiates the request to the AS.

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

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

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

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   Content-type: application/json

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

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

   If the user scans the code, they are taken to the interaction
   endpoint and the AS looks up the current pending request based on the
   incoming URL.  If the user instead goes to the static page and enters
   the code manually, the AS looks up the current pending request based
   on the value of the user code.  In both cases, the user logs in, is
   identified as the RO for the resource being requested, and approves
   the request.  Once the request has been approved, the AS displays to
   the user a message to return to their device.

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

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

   {
       "handle": "80UPRY5NM33OMUKMKSKU"
   }

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

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   Content-type: application/json

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

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

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

   {
       "handle": "BI9QNW6V9W3XFJK4R02D"
   }

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

Content-type: application/json

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

Appendix D.  No User Involvement

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

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

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

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

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

Content-type: application/json

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L",
        "resources": [
            "backend service", "nightly-routine-3"
        ]
    }
}

D.1.  Asynchronous Authorization

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

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

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

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

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

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   Content-type: application/json

   {
       "continue": {
           "handle": "80UPRY5NM33OMUKMKSKU",
           "uri": "https://server.example.com/continue",
           "wait": 60
       }
   }

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

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

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

   {
       "handle": "80UPRY5NM33OMUKMKSKU"
   }

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

   Content-type: application/json

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

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

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

   {
       "handle": "BI9QNW6V9W3XFJK4R02D"
   }

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

Content-type: application/json

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

D.2.  Applying OAuth 2 Scopes and Client IDs

   In this scenario, the client developer has a client_id and set of
   scope values from their OAuth 2 [RFC6749] system and wants to apply
   them to the new protocol.  Traditionally, the OAuth 2 client
   developer would put their client_id and scope values as parameters
   into a redirect request to the authorization endpoint.

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

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

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

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

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

   From here, the protocol continues as above.

Author's Address

   Justin Richer (editor)
   Bespoke Engineering

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

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