Internet-Draft Grant Negotiation Access Protocol September 2020
Richer Expires March 15, 2021 [Page]
Workgroup:
GNAP
Internet-Draft:
draft-richer-transactional-authz-11
Published:
Intended Status:
Standards Track
Expires:
Author:
J. Richer, Ed.
Bespoke Engineering

Grant Negotiation Access Protocol

Abstract

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

This document has been prepared by the GNAP working group design team of Kathleen Moriarty, Fabien Imbault, Dick Hard, Mike Jones, and Justin Richer. This document is input into the GNAP working group.

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 March 15, 2021.

Table of Contents

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.

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

1.1. Roles

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

Authorization Server (AS)
Manages the requested delegations for the RO. The AS issues tokens and directly delegated information to the RC. The AS is defined by its grant endpoint, a single URL that accepts a POST request with a JSON payload. The AS could also have other endpoints, including interaction endpoints and user code endpoints, and these are introduced to the RC as needed during the delegation process.
Resource Client (RC, aka "client")
Requests tokens from the AS and uses tokens at the RS. 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 RC, including what it can request and on whose behalf.
Resource Server (RS)
Accepts tokens from the RC issued by the AS and serves delegated resources on behalf of the RO. There could be multiple RSs protected by the AS that the RC will call.
Resource Owner (RO)
Authorizes the request from the RC to the RS, often interactively at the AS.
Requesting Party (RQ, aka "user")
Operates and interacts with the RC.

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

Multiple roles can be fulfilled by the same party, and a given party can switch roles in different instances of the protocol. For example, the RO and RQ in many instances are the same person, where a user is authorizing the RC to act on their own behalf at the RS. In this case, one party fulfills both of the RO and RQ roles, but the roles themselves are still defined separately from each other to allow for other use cases where they are fulfilled by different parties.

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

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

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

[[ Editor's note: The names for the roles are an area of ongoing discussion within the working group, as is the appropriate precision of what activities and expectations a particular role covers. In particular, the AS might be formally decomposed into delegation components, that the client talks to, and interaction components, that the user talks to. ]]

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.

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)--|               |       |            |
        |        |--------------(6)------------->|            |
        |        |       |               |<-(7)--|            |
        |        |<-------------(8)------------->|            |
        |        |--(9)->|               |       |            |
        |        |<-(10)-|               |       |            |
        |        |--------------(11)------------>|            |
        |        |       |               |<-(12)-|            |
        |        |-(13)->|               |       |            |
        |        |       |               |       |            |
        +--------+       +---------------+       +------------+

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

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.

    +--------+                                  +--------+         +------+
    |   RC   |                                  |   AS   |         |  RO  |
    |        |                                  |        |         |  +   |
    |        |< (1) + Start Session + + + + + + + + + + + + + + + +|  RQ  |
    |        |                                  |        |         |(User)|
    |        |--(2)--- Request Access --------->|        |         |      |
    |        |                                  |        |         |      |
    |        |<-(3)-- Interaction Needed -------|        |         |      |
    |        |                                  |        |         |      |
    |        |+ (4) + Redirect for Interaction + + + + + + + + + > |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (5) +>|      |
    |        |                                  |        |  AuthN  |      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (6) +>|      |
    |        |                                  |        |  AuthZ  |      |
    |        |                                  |        |         |      |
    |        |< (7) + Redirect for Continuation + + + + + + + + + +|      |
    |        |                                  |        |         +------+
    |        |--(8)--- Continue Request ------->|        |
    |        |                                  |        |
    |        |<-(9)----- Grant Access ----------|        |
    |        |                                  |        |
    +--------+                                  +--------+
  1. The RC establishes a verifiable session to the user, in the role of the RQ.
  2. The RC requests access to the resource (Section 2). The RC indicates that it can redirect to an arbitrary URL (Section 2.5.1) and receive a callback from the browser (Section 2.5.3). The RC stores verification information for its callback in the session created in (1).
  3. The AS determines that interaction is needed and responds (Section 3) with a URL to send the user to (Section 3.3.1) and information needed to verify the callback (Section 3.3.3) in (7). The AS also includes information the RC will need to continue the request (Section 3.1) in (8). The AS associates this continuation information with an ongoing request that will be referenced in (4), (6), and (8).
  4. The RC stores the verification and continuation information from (3) in the session from (1). The RC then redirects the user to the URL (Section 4.1) given by the AS in (3). The user's browser loads the interaction redirect URL. The AS loads the pending request based on the incoming URL generated in (3).
  5. The user authenticates at the AS, taking on the role of the RO.
  6. As the RO, the user authorizes the pending request from the RC.
  7. When the AS is done interacting with the user, the AS redirects the user back (Section 4.4.1) to the RC using the callback URL provided in (2). The callback URL is augmented with an interaction reference that the AS associates with the ongoing request created in (2) and referenced in (4). The callback URL is also augmented with a hash of the security information provided in (2) and (3). The RC loads the verification information from (2) and (3) from the session created in (1). The RC calculates a hash (Section 4.4.3) based on this information and continues only if the hash validates. Note that the RC needs to ensure that the parameters for the incoming request match those that it is expecting from the session created in (1). The RC also needs to be prepared for the RQ never being returned to the RC and handle time outs appropriately.
  8. The RC loads the continuation information from (3) and sends the interaction reference from (7) in a request to continue the request (Section 5.1). The AS validates the interaction reference ensuring that the reference is associated with the request being continued.
  9. If the request has been authorized, the AS grants access to the information in the form of access tokens (Section 3.2) and direct subject information (Section 3.4) to the RC.

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

1.2.2. User-code Interaction

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

    +--------+                                  +--------+         +------+
    |   RC   |                                  |   AS   |         |  RO  |
    |        |--(1)--- Request Access --------->|        |         |  +   |
    |        |                                  |        |         |  RQ  |
    |        |<-(2)-- Interaction Needed -------|        |         |(User)|
    |        |                                  |        |         |      |
    |        |+ (3) + + Display User Code + + + + + + + + + + + + >|      |
    |        |                                  |        |         |      |
    |        |                                  |        |<+ (4) +>|      |
    |        |                                  |        |  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).
  4. The user's directs their browser to the user code URL. This URL is stable and can be communicated via the RC's documentation, the AS documentation, or the RC software itself. Since it is assumed that the RO will interact with the AS through a secondary device, the RC does not provide a mechanism to launch the RO's browser at this URL. 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 RO 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). Note that the AS may need to determine that the RO has not approved the request in a sufficient amount of time and return an appropriate error to the RC.
  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.

    +--------+                                  +--------+         +------+
    |   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 RO, the AS indicates to the RO that the request has been completed.
  6. Meanwhile, the RC loads the continuation information stored at (3) and continues the request (Section 5). The AS determines which ongoing access request is referenced here and checks its state.
  7. If the access request has not yet been authorized by the RO in (6), the AS responds to the RC to continue the request (Section 3.1) at a future time through additional polling. This response can include refreshed credentials as well as information regarding how long the RC should wait before calling again. The RC replaces its stored continuation information from the previous response (2). Note that the AS may need to determine that the RO has not approved the request in a sufficient amount of time and return an appropriate error to the RC.
  8. The RC continues to poll the AS (Section 5) with the new continuation information from (7).
  9. If the request has been authorized, the AS grants access to the information in the form of access tokens (Section 3.2) and direct subject information (Section 3.4) to the RC.

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

1.2.4. 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. 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.

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).

2. Requesting Access

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

resources
Describes the rights that the RC is requesting for one or more access tokens to be used at RS's. Section 2.1
subject
Describes the information about the RO that the RC is requesting to be returned directly in the response from the AS. Section 2.2
key
Identifies the key that the RC will use to protect this request and any continuation requests at the AS. Section 2.3
user
Identifies the RQ to the AS in a manner that the AS can verify, either directly or by interacting with the RQ to determine their status as the RO. Section 2.4
interact
Describes the capabilities that the RC has for allowing the RO to interact with the AS. Section 2.5
display
Describes the user-facing information about the RC used in interactions at the AS. Section 2.6
capabilities
Identifies named extension capabilities that the RC can use, signaling to the AS which extensions it can use. Section 2.7
existing_grant
Identifies a previously-existing grant that the RC is extending with this request. Section 2.8
claims
Identifies the identity claims to be returned as part of an OpenID Connect claims request. Section 2.9

Additional members of this request object can be defined by extensions to this protocol as described in Section 2.10

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

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

2.1. Requesting Resources

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

2.1.1. Requesting a Single Access Token

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

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

type
The type of resource request as a string. This field MAY define which other elements are allowed in the request. This element is REQUIRED.

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

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

[[ 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. For example, an RC asking for a combination of "read" and "write" access.
locations
The location of the RS as an array of strings. These strings are typically URIs identifying the location of the RS.
datatypes
The kinds of data available to the RC at the RS's API as an array of strings. For example, an RC asking for access to raw "image" data and "metadata" at a photograph API.
identifier
A string identifier indicating a specific resource at the RS. For example, a patient identifier for a medical API or a bank account number for a financial API.

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

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

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

2.1.2. Requesting Resources By Reference

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

[[ 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 RC and MAY be any valid JSON string, and therefore could include spaces, unicode characters, and properly escaped string sequences. However, in some situations the value is intended to be seen and understood be the RC developer. In such cases, the API designer choosing any such human-readable strings SHOULD take steps to ensure the string values are not easily confused by a developer

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

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

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

[[ Editor's note: passing resource requests by reference really is akin to a "scope", and we have many years of experience showing us that the simplicity of giving a developer a set of strings to send is a simple and powerful pattern. We could always require objects and just use the "type" field as a scope value, but that's a lot of complexity to pay for the simple case. Client developers will always know which kind they need to send, because they're the ones picking from the API's description. ]]

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 RC, 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.

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

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

2.2. Requesting User Information

If the RC is requesting information about the RO 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 RO, as defined by [I-D.ietf-secevent-subject-identifiers].
assertions
An array of requested assertion formats. Possible values include id_token for an [OIDC] ID Token and saml2 for a SAML 2 assertion. Additional assertion values are defined by a registry TBD (Section 12). [[ Editor's note: These values are lifted from [RFC8693]'s "token type identifiers" list, but is there a better source?]]
"subject": {
   "sub_ids": [ "iss-sub", "email" ],
   "assertions": [ "id_token", "saml2" ]
}

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

Note: 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 types 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 RC by Key

When sending a non-continuation request to the AS, the RC MUST identify itself by including the key field in the request and by signing the request as described in Section 8.

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 [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 RC

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

The presentation of a key allows the AS to strongly associate multiple successive requests from the same RC with each other. This is true when the AS knows the key ahead of time and can use the key to authenticate the RC software, but also if the key is ephemeral and created just for this request. As such the AS MAY allow for RCs to make requests with unknown keys. This pattern allows for ephemeral RCs, such as single-page applications, and RCs with many individual instances, such as mobile applications, to generate their own key pairs and use them within the protocol without having to go through a separate registration step. The AS MAY limit which capabilities are made available to RCs with unknown keys. For example, the AS could have a policy saying that only previously-registered RCs can request particular resources, or that all RCs with unknown keys have to be interactively approved by an RO.

2.3.2. Identifying the Client Key By Reference

If the RC has a reference for its key, the RC MAY send that reference handle as a string. The format of this string is determined by the AS and is opaque to the RC.

  "key": "7C7C4AZ9KHRS6X63AJAO"

If the key is passed by reference, the proofing mechanism associated with that key reference MUST also be used by the RC, 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 RC identifies its key by reference, the referenced key MAY be a symmetric key known to the AS. The RC MUST NOT send a symmetric key by value in the request, as doing so would expose the key directly instead of proving possession of it.

[[ 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 registration and authentication process. See Appendix D.2 for an example. Something like this is required to make things easier for client developers in the common case where the AS already knows the client's key, and to allow symmetric keys. ]]

2.4. Identifying the User

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

sub_ids
An array of subject identifiers for the RQ, as defined by [I-D.ietf-secevent-subject-identifiers].
assertions
An object containing assertions as values keyed on the assertion type defined by a registry TBD (Section 12). Possible keys include id_token for an [OIDC] ID Token and saml2 for a SAML 2 assertion. Additional assertion values are defined by a registry TBD (Section 12). [[ Editor's note: These keys are lifted from [RFC8693]'s "token type identifiers" list, but is there a better source? Additionally: 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": {
     "id_token": "eyj..."
   }
}

Subject identifiers are hints to the AS in determining the RO and MUST NOT be taken as declarative statements that a particular RO is present at the RC and acting as the RQ. Assertions SHOULD be validated by the AS. [[ editor's note: is this a MUST? Assertion validation is extremely specific to the kind of assertion in place, what other guidance and requirements can we put in place here? ]]

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

[[ 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. The security parameters are pretty different here. ]]

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

2.4.1. Identifying the User by Reference

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

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

"user": "XUT2MFM1XBIKJKSDU8QM"

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

[[ Editor's note: we might be able to fold this function into an unstructured user assertion reference issued by the AS to the RC. We could put it in as an assertion type of "gnap_reference" or something like that. Downside: it's more verbose and potentially confusing to the client developer to have an assertion-like thing that's internal to the AS and not an assertion. ]]

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

2.5. Interacting with the User

If the RC is capable of driving interaction with the RQ, and the client presumes the RQ can act as the RO, the RC 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 RC MUST NOT declare an interaction capability it does not support.

The RC 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. This specification defines the following interaction capabilities:

<spanx style="verb">redirect</spanx>
Indicates that the RC can direct the RQ to an arbitrary URL at the AS for interaction. Section 2.5.1
<spanx style="verb">app</spanx>
Indicates that the RC can launch an application on the RQ's device for interaction. Section 2.5.2
<spanx style="verb">callback</spanx>
Indicates that the RC can receive a callback from the AS after interaction with the RO has concluded. Section 2.5.3
<spanx style="verb">user_code</spanx>
Indicates that the RC can communicate a human-readable short code to the RQ for use with a stable URL at the AS. Section 2.5.4
<spanx style="verb">ui_locales</spanx>
Indicates the RQ's preferred locales that the AS can use during interaction, particularly before the RO has authenticated. Section 2.5.5

The following sections detail requests for interaction 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. ]]

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

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

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

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

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

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

2.5.1. Redirect to an Arbitrary URL

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

"interact": {
   "redirect": true
}

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

2.5.1.1. Redirect to an Arbitrary Shortened URL

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

"interact": {
   "redirect": 255
}

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

2.5.2. Open an Application-specific URL

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

"interact": {
   "app": true
}

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

uri
REQUIRED. Indicates the URI to send the RO to after interaction. This URI MAY be unique per request and MUST be hosted by or accessible by the RC. This URI MUST NOT contain any fragment component. This URI MUST be protected by HTTPS, be hosted on a server local to the RO's browser ("localhost"), or use an application-specific URI scheme. If the RC needs any state information to tie to the front channel interaction response, it MUST use a unique callback URI to link to that ongoing state. The allowable URIs and URI patterns MAY be restricted by the AS based on the RC's presented key information. The callback URI SHOULD be presented to the RO during the interaction phase before redirect.
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 contact the RC. Valid values include redirect Section 2.5.3.1 and push Section 2.5.3.2, with other values defined by a registry TBD (Section 12).
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 RC and request, the AS returns a nonce for use in validating the callback response (Section 3.3.3). Requests to the callback URI MUST be processed as described in Section 4.4, and the AS MUST require presentation of an interaction callback reference as described in Section 5.1.

2.5.3.1. Receive an HTTP Callback Through the Browser

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

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

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

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

2.5.3.2. Receive an HTTP Direct Callback

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

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

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

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

2.5.4. Display a Short User Code

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

"interact": {
    "user_code": true
}

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

2.5.5. Indicate Desired Interaction Locales

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

"interact": {
    "ui_locales": ["en_US", "fr_CA"]
}

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

2.5.6. Extending Interaction Capabilities

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

[[ 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 like DIDCOMM and challenge-response protocols like FIDO, for example. ]]

2.6. Providing Displayable RC Information

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

name
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"
    }

[[ Editor's note: would we want to support pushing a display logo by value? On the upside it allows for more dynamic detached clients and doesn't require the AS to fetch information. On the downside, this is harder for the AS to enforce a policy about and could lead to potential exploits caused by sending binary image files. ]]

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

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

[[ 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 RC Capabilities

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

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

2.8. Referencing an Existing Grant Request

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

"existing_grant": "80UPRY5NM33OMUKMKSKU"

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

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

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

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

Note that because this is an independent query object, the claims value can augment or alter other portions of the request, namely the resources and subject fields. This query language uses the fields in the top level of the object to indicate the target for any requested claims. For instance, the userinfo target indicates that 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.

[[ 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 in an extension. 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 extension item affects or influences the values or behavior of other request and response objects.

[[ Editor's note: we should have more guidance and examples on what possible top-level extensions would look like. ]]

3. Grant Response

In response to a RC'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 a bearer access token (Section 3.2.1) with a management URL and a subject identifier (Section 3.4) in the form of an email address.

{
    "access_token": {
        "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
        "proof": "bearer",
        "manage": "https://server.example.com/token/PRY5NM33OM4TB8N6BW7OZB8CDFONP219RP1L"
    },
    "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 continuing the request.
uri
REQUIRED. The URI at which the RC can make continuation requests. This URI MAY vary per RC or ongoing request, or MAY be stable at the AS. The RC MUST use this value exactly as given when making a continuation request (Section 5).
wait
RECOMMENDED. The amount of time in integer seconds the RC 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 RC MUST NOT use the handle past this time. The AS MUST respond to an expired handle with an error. Note that the handle MAY be revoked at any point prior to its expiration.
{
    "continue": {
        "handle": "80UPRY5NM33OMUKMKSKU",
        "uri": "https://server.example.com/continue",
        "wait": 60
    }
}

The RC can use the values of this field to continue the request as described in Section 5.

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

[[ Editor's note: The combination of a "handle" and "uri" really feels like the access token pattern. Perhaps the exact constructs for tokens could be re-used here instead of something special for the request continuation? Especially if we're using some kind of directed access token mechanism. ]]

3.2. Access Tokens

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

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

value
REQUIRED. The value of the access token as a string. The value is opaque to the RC. The value SHOULD be limited to ASCII characters to facilitate transmission over HTTP headers within other protocols without requiring additional encoding.
proof
REQUIRED. The proofing presentation mechanism used for presenting this access token to an RS. See 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 RC MAY manage its access token as described in Section 6. This management URI is a function of the AS and is separate from the RS the RC is requesting access to. This URI MUST NOT include the access token value and SHOULD be different for each access token issued in a request.
resources
OPTIONAL. A description of the rights associated with this access token, as defined in 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 RC.
expires_in
OPTIONAL. The number of seconds in which the access will expire. The RC MUST NOT use the access token past this time. An RS MUST NOT accept an access token past this time. Note that the access token MAY be revoked by the AS or RS at any point prior to its expiration.
key
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? ]]

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

    "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"
        ]
    }

If the RC requested multiple access tokens (Section 2.1.3), the AS MUST NOT respond with a single access token structure.

[[ Editor's note: There has been interest in describing a way for the AS to tell the client both how and where to use the token. This kind of directed access token could allow for some interesting deployment patterns where the client doesn't know much]]

3.2.2. Multiple Access Tokens

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

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

    "multiple_access_tokens": {
        "token1": {
            "value": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
            "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 RC's request. The AS MAY refuse to issue one or more of the requested access tokens. In such cases all of the other issued access tokens are included in the response except for 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 RC 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 management is allowed, each access token SHOULD have different management URIs.

[[ Editor's note: Do we need to specify that the management URIs are different if we require the token to be presented? ]]

3.3. Interaction Capabilities

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

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

3.3.1. Redirection to an arbitrary URL

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

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

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

[[ Editor's note: This is one aspect where the AS might actually be two separate roles. Namely, a delegation server (back end) and interaction server (user-facing).]]

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

3.3.2. Launch of an application URL

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

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

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

[[ 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 URL

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

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

[[ Editor's note: This is fairly parallel to the request but it kinda hides the fact that this is a nonce from the AS, not the client. ]]

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

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

3.3.4. Display of a Short User Code

If the RC indicates that it can display a short user-typeable code (Section 2.5.4) and the AS supports this capability for the RC'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 RCs can be statically configured with it.
    "interact": {
        "user_code": {
            "code": "A1BC-3DFF",
            "url": "https://srv.ex/device"
        }
    }

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

The RC SHOULD also communicate the URL if possible to facilitate user interaction, but since the URL should be stable, the RC should be able to safely decide to not display this value. As this interaction capability is designed to facilitate interaction via a secondary device, it is not expected that the RC redirect the RQ to the URL given here at runtime. Consequently, the URL needs to be stable enough that a RC could be statically configured with it, perhaps referring the RQ to the URL via documentation instead of through an interactive means. If the RC is capable of communicating an arbitrary URL to the RQ, such as through a scannable code, the RC can use the "redirect" (Section 2.5.1) capability for this purpose instead of or in addition to the user code capability.

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

[[ Editor's note: This is one aspect where the AS might actually be two separate roles. Namely, a delegation server (back end) and interaction server (user-facing).]]

3.3.5. Extending Interaction Capability Responses

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

3.4. Returning User Information

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

sub_ids
An array of subject identifiers for the RO, 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 RC MAY use this value to determine if it needs to request updated profile information through an identity API. The definition of such an identity API is out of scope for this specification.
"subject": {
   "sub_ids": [ {
     "subject_type": "email",
     "email": "user@example.com",
   } ],
   "assertions": {
     "id_token": "eyj..."
   }
}

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

3.5. Returning Dynamically-bound Reference Handles

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

Some references, such as for the RC's keys (Section 2.3.2) or the requested resources (Section 2.1.2), can be managed statically through an admin console or developer portal provided by the AS or RS. If desired, the AS MAY also generate and return some of these references dynamically to the RC in its response to facilitate multiple interactions with the same software. The RC SHOULD use these references in future requests in lieu of sending the associated data value. These handles are intended to be used on future requests.

Dynamically generated handles are string values that MUST be protected by the RC as secrets. Handle values MUST be unguessable and MUST NOT contain any sensitive information. Handle values are opaque to the RC. [[ 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 RC can use in a future request, as described in Section 2.3.2.
user_handle
A value used to represent the current user. The RC can use in a future request, as described in Section 2.4.1.

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

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

[[ Editor's note: the ability to dynamically return reference handles allows for an inline version of dynamic registration without needing to go through a discrete registration step, for clients where that makes sense. Currently this is entirely up to the AS to decide when to issue these, but maybe the client should signal that it can receive these handles as part of the request? Since the client is the component that will know if it's in a position to make use of such reference handles in the future (like a mobile app) or if it's just going to evaporate at the end of a session (like an SPA). Ultimately we need to deal with a range of dynamism, not just the "pre-registered" vs. "non-registered" use cases that OAuth forces us in to. ]]

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 RC indicates that it is capable of driving interaction with the RO in its request (Section 2.5), and the AS determines that interaction is required and responds to one or more of the RC's interaction capabilities, the RC 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:

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

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

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

4.2. Interaction at the User Code URI

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

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

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

4.3. Interaction through an Application URI

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

[[ 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 RO, 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 RC to continue. If this capability is not available, the AS SHOULD instruct the RO to return to their RC software upon completion. Note that these steps still take place in most error cases, such as when the RO has denied access. This pattern allows the RC to potentially recover from the error state without restarting the request from scratch.

[[ 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 RC 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.

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

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

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

hash
REQUIRED. The interaction hash value as described in Section 4.4.3.
interact_ref
REQUIRED. The interaction reference generated for this interaction.

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

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

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

4.4.2. Completing Interaction with a Direct HTTP Request Callback

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

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

hash
REQUIRED. The interaction hash value as described in Section 4.4.3.
interact_ref
REQUIRED. The interaction reference generated for this interaction.
POST /push/554321 HTTP/1.1
Host: client.example.net
Content-Type: application/json

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

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

4.4.3. Calculating the interaction hash

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

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

VJLO6A4CAYLBXHTR0KRO
MBDOFXG4Y5CVJCX821LH
4IFWWIKYBC2PQ6U56NL1

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

[[ 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. ]]

4.4.3.1. SHA3-512

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

p28jsq0Y2KK3WS__a42tavNC64ldGTBroywsWxT4md_jZQ1R2HZT8BOWYHcLmObM7XHPAdJzTZMtKBsaraJ64A
4.4.3.2. SHA2-512

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

62SbcD3Xs7L40rjgALA-ymQujoh2LB2hPJyX9vlcr1H6ecChZ8BNKkG_HrOKP_Bpj84rh4mC9aE9x7HPBFcIHw

5. Continuing a Grant Request

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

{
  "handle": "tghji76ytghj9876tghjko987yh"
}

The RC 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 RC MUST NOT call the continuation URI prior to waiting the number of seconds indicated. If no "wait" period is indicated, the RC SHOULD wait at least 5 seconds [[ Editor's note: what's a reasonable amount of time so as not to DOS the server?? ]]. If the RC does not respect the given wait period, the AS MUST return an error.

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

If the AS determines that the RC 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 RC MUST NOT make an additional continuation request. If a RC does so, the AS MUST return an error.

If the AS determines that the RC still needs to drive interaction with the RQ, the AS MAY return appropriate responses for any of the interaction mechanisms (Section 3.3) the RC 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 RC 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 RC's key as described in Section 2.3.1.

5.1. Continuing after a Finalized Interaction

If the RC has received an interaction reference from a "callback" (Section 4.4.1) message, the RC MUST include the "interaction_ref" in its continuation request. The RC MUST validate the hash before making the continuation request, but note that the RC 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 RC's original request. The AS SHOULD revoke existing access tokens. If the AS determines that the RC 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 RC MUST NOT make an additional continuation request. If the RC does so, the AS MUST return an error.

[[ Editor's note: There is significant overlap here with the functionality that allows the rotation of an individual access token in the next main section. It seems like this would still be needed to modify the entire request, but for the common case where you've got a single access token in the response, you've got two ways to do almost the same thing, which is confusing for client developers. We need to discuss how best to manage these patterns in concert with each other. ]]

6. Token Management

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

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

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

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

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

6.1. Rotating the Access Token

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

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

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

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

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

{
    "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"
        ]
    }
}

[[ Editor's note: If the client is using its own key as the proof, like with a bearer access token, the AS is going to need to know if the client's key has been rotated. We don't have a mechanism for rotating the token's key or the client's key yet either - so that could occur through this management function as well. ]]

6.2. Revoking the Access Token

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

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

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

If the token was issued to the RC identified by the key, the AS MUST invalidate the access token, if possible, and return an HTTP 204 response code.

204 No Content

If the access token has expired, the AS SHOULD honor the revocation request to the token management URL as valid, since the end result is still the token not being usable.

Though the AS MAY revoke an access token at any time for any reason, the token management function is specifically for the RC's use.

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

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

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. Perhaps 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 it was in 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
httpsig
HTTP Signing signature header
oauthpop
OAuth PoP key proof authentication header

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

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

When used in the GNAP delegation protocol, these key binding mechanisms allow the AS to ensure that the keys presented by the RC in the initial request are in control of the party calling any follow-up or continuation requests. To facilitate this requirement, all keys in the initial request Section 2.3 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 request for each call within that request.

[[ Editor's note: We are going to need a way for a client to rotate its keys securely, even while an ongoing grant is in effect. ]]

8.1. Detached JWS

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

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

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

htm
The HTTP Method used to make this request, as an uppercase ASCII string.
htu
The HTTP URI used for this request, including all path and query components.
ts
A timestamp of the request in integer seconds

[[ Editor's note: It's not the usual practice to put additional information into the header of a JWS, but this keeps us from having to normalize the body serialization. ]]

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

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

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

[[ 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 jwsd in the proof field. A JWS [RFC7515] signature object is created as follows:

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

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

htm
The HTTP Method used to make this request, as an uppercase ASCII string.
htu
The HTTP URI used for this request, including all path and query components.
ts
A timestamp of the request in integer seconds

[[ Editor's note: It's not the usual practice to put additional information into the header of a JWS, but this keeps us from having to modify the body to use this signature method. ]]

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

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

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

eyJiNjQiOmZhbHNlLCJhbGciOiJSUzI1NiIsImtpZCI6Inh5ei0xIn0.ewogICAgIm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.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. ]]

8.3. Mutual TLS

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

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

{
    "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": "mtls",
        "cert": "MIIEHDCCAwSgAwIBAgIBATANBgkqhkiG9w0BAQsFADCBmjE3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"
    }
}

[[ Editor's note: ]]

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. In addition to the required fields, the DPoP body MUST also contain a digest of the request body:

digest
Digest of the request body as the value of the Digest header defined in [RFC3230].
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
DPoP: eyJ0eXAiOiJkcG9wK2p3dCIsImFsZyI6IlJTMjU2IiwiandrIjp7Imt0eSI6Il
JTQSIsImUiOiJBUUFCIiwia2lkIjoieHl6LWNsaWVudCIsImFsZyI6IlJTMjU2Iiwibi
I6Inp3Q1RfM2J4LWdsYmJIcmhlWXBZcFJXaVk5SS1uRWFNUnBablJySWpDczZiX2VteV
RrQmtEREVqU3lzaTM4T0M3M2hqMS1XZ3hjUGRLTkdaeUlvSDNRWmVuMU1LeXloUXBMSk
cxLW9MTkxxbTdwWFh0ZFl6U2RDOU8zLW9peXk4eWtPNFlVeU5aclJSZlBjaWhkUUNiT1
9PQzhRdWdtZzlyZ05ET1NxcHBkYU5lYXMxb3Y5UHhZdnhxcnoxLThIYTdna0QwMFlFQ1
hIYUIwNXVNYVVhZEhxLU9fV0l2WVhpY2c2STVqNlM0NFZOVTY1VkJ3dS1BbHluVHhRZE
1BV1AzYll4VlZ5NnAzLTdlVEpva3ZqWVRGcWdEVkRaOGxVWGJyNXlDVG5SaG5oSmd2Zj
NWakRfbWFsTmU4LXRPcUs1T1NEbEhUeTZnRDlOcWRHQ20tUG0zUSJ9fQ.eyJodHRwX21
ldGhvZCI6IlBPU1QiLCJodHRwX3VyaSI6Imh0dHA6XC9cL2hvc3QuZG9ja2VyLmludGV
ybmFsOjk4MzRcL2FwaVwvYXNcL3RyYW5zYWN0aW9uIiwiaWF0IjoxNTcyNjQyNjEzLCJ
qdGkiOiJIam9IcmpnbTJ5QjR4N2pBNXl5RyJ9.aUhftvfw2NoW3M7durkopReTvONng1
fOzbWjAlKNSLL0qIwDgfG39XUyNvwQ23OBIwe6IuvTQ2UBBPklPAfJhDTKd8KHEAfidN
B-LzUOzhDetLg30yLFzIpcEBMLCjb0TEsmXadvxuNkEzFRL-Q-QCg0AXSF1h57eAqZV8
SYF4CQK9OUV6fIWwxLDd3cVTx83MgyCNnvFlG_HDyim1Xx-rxV4ePd1vgDeRubFb6QWj
iKEO7vj1APv32dsux67gZYiUpjm0wEZprjlG0a07R984KLeK1XPjXgViEwEdlirUmpVy
T9tyEYqGrTfm5uautELgMls9sgSyE929woZ59elg

{
    "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": "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. ]]

8.5. HTTP Signing

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

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

{
    "display": {
        "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-
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 omitted unless this method is being used in conjunction with an access token as in Section 7. [[ Editor's note: this is in contradiction to the referenced spec which makes this field mandatory. ]]
  • The b (body hash) field MUST be calculated and supplied
  • All components of the URL MUST be calculated and supplied
  • The m (method) field MUST be supplied
POST /tx HTTP/1.1
Host: server.example.com
Content-Type: application/json
PoP: eyJhbGciOiJSUzI1NiIsImp3ayI6eyJrdHkiOiJSU0EiLCJlIjoi
QVFBQiIsImtpZCI6Inh5ei1jbGllbnQiLCJhbGciOiJSUzI1NiIsIm4iO
iJ6d0NUXzNieC1nbGJiSHJoZVlwWXBSV2lZOUktbkVhTVJwWm5ScklqQ3
M2Yl9lbXlUa0JrRERFalN5c2kzOE9DNzNoajEtV2d4Y1BkS05HWnlJb0g
zUVplbjFNS3l5aFFwTEpHMS1vTE5McW03cFhYdGRZelNkQzlPMy1vaXl5
OHlrTzRZVXlOWnJSUmZQY2loZFFDYk9fT0M4UXVnbWc5cmdORE9TcXBwZ
GFOZWFzMW92OVB4WXZ4cXJ6MS04SGE3Z2tEMDBZRUNYSGFCMDV1TWFVYW
RIcS1PX1dJdllYaWNnNkk1ajZTNDRWTlU2NVZCd3UtQWx5blR4UWRNQVd
QM2JZeFZWeTZwMy03ZVRKb2t2allURnFnRFZEWjhsVVhicjV5Q1RuUmhu
aEpndmYzVmpEX21hbE5lOC10T3FLNU9TRGxIVHk2Z0Q5TnFkR0NtLVBtM
1EifX0.eyJwIjoiXC9hcGlcL2FzXC90cmFuc2FjdGlvbiIsImIiOiJxa0
lPYkdOeERhZVBTZnc3NnFjamtqSXNFRmxDb3g5bTU5NFM0M0RkU0xBIiw
idSI6Imhvc3QuZG9ja2VyLmludGVybmFsIiwiaCI6W1siQWNjZXB0Iiwi
Q29udGVudC1UeXBlIiwiQ29udGVudC1MZW5ndGgiXSwiVjQ2OUhFWGx6S
k9kQTZmQU5oMmpKdFhTd3pjSGRqMUloOGk5M0h3bEVHYyJdLCJtIjoiUE
9TVCIsInRzIjoxNTcyNjQyNjEwfQ.xyQ47qy8bu4fyK1T3Ru1Sway8wp6
5rfAKnTQQU92AUUU07I2iKoBL2tipBcNCC5zLH5j_WUyjlN15oi_lLHym
fPdzihtt8_Jibjfjib5J15UlifakjQ0rHX04tPal9PvcjwnyZHFcKn-So
Y3wsARn-gGwxpzbsPhiKQP70d2eG0CYQMA6rTLslT7GgdQheelhVFW29i
27NcvqtkJmiAG6Swrq4uUgCY3zRotROkJ13qo86t2DXklV-eES4-2dCxf
cWFkzBAr6oC4Qp7HnY_5UT6IWkRJt3efwYprWcYouOVjtRan3kEtWkaWr
G0J4bPVnTI5St9hJYvvh7FE8JirIg

{
    "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": "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"
        }
    }
}

[[ Editor's note: This is a stale draft from the OAuth working group, but it does at least provide some basic functionality for protecting HTTP messages with a signature. This work is likely to be subsumed by the general-purpose HTTP message signature mechanism in Section 8.5. ]]

9. Discovery

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

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

grant_request_endpoint
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 RC can be registered with the mtls key proofing mechanism, but the AS also returns other proofing methods, then the AS will deny a request from that RC using a different proofing mechanism.

10. Resource Servers

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

[[ 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 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 the RS's keys instead of the RC's or token's keys. ]]

+------+       +------+       +------+
|  RC  |--(1)->|  RS  |       |  AS  |
|      |       |      |--(2)->|      |
|      |       |      |<-(3)--|      |
|      |       |      |       +------+
|      |<-(4)--|      |
+------+       +------+
  1. The RC calls the RS with its access token.
  2. The RS introspects the access token value at the AS. The RS signs the request with its own key (not the RC's key or the token's key).
  3. The AS validates the token value and the RC's request and returns the introspection response for the token.
  4. The RS fulfills the request from the RC.

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

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

{
    "access_token": "OS9M2PMHKUR64TB8N6BW7OZB8CDFONP219RP1LT0",
}

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

Content-type: application/json

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

10.2. Deriving a downstream token

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

+------+       +-------+       +------+       +-------+
|  RC  |--(1)->|  RS1  |       |  AS  |       |  RS2  |
|      |       |       |--(2)->|      |       |       |
|      |       |       |<-(3)--|      |       |       |
|      |       |       |       +------+       |       |
|      |       |       |                      |       |
|      |       |       |-----------(4)------->|       |
|      |       |       |<----------(5)--------|       |
|      |<-(6)--|       |                      |       |
+------+       +-------+                      +-------+
  1. The RC calls RS1 with an access token.
  2. RS1 presents that token to the AS to get a derived token for use at RS2. RS1 indicates that it has no ability to interact with the RO. RS1 signs its request with its own key, not the token's key or the RC's key.
  3. The AS returns a derived token to RS1 for use at RS2.
  4. RS1 calls RS2 with the token from (3).
  5. RS2 fulfills the call from RS1.
  6. RS1 fulfills the call from RC.

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

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

[[ Editor's note: this is similar to Section 2.8 but based on the access token and not the grant. We might be able to re-use that function: 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, but there might be some subtle security issues there. ]]

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.

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 (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. ]]

10.4. Requesting a Resources With Insufficient Access

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

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

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

[[ 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. ]]

13. Security Considerations

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

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

14. Privacy Considerations

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

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

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

15. Normative References

[BCP195]
"Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", , <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, , <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, , <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, , <http://www.ietf.org/internet-drafts/draft-ietf-oauth-signed-http-request-03.txt>.
[I-D.ietf-secevent-subject-identifiers]
Backman, A. and M. Scurtescu, "Subject Identifiers for Security Event Tokens", Work in Progress, Internet-Draft, draft-ietf-secevent-subject-identifiers-06, , <http://www.ietf.org/internet-drafts/draft-ietf-secevent-subject-identifiers-06.txt>.
[OIDC]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and C. Mortimore, "OpenID Connect Core 1.0 incorporating errata set 1", , <https://openiD.net/specs/openiD-connect-core-1_0.html>.
[OIDC4IA]
Lodderstedt, T. and D. Fett, "OpenID Connect for Identity Assurance 1.0", , <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, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC3230]
Mogul, J. and A. Van Hoff, "Instance Digests in HTTP", RFC 3230, DOI 10.17487/RFC3230, , <https://www.rfc-editor.org/info/rfc3230>.
[RFC5646]
Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, , <https://www.rfc-editor.org/info/rfc5646>.
[RFC6749]
Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, , <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, , <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, , <https://www.rfc-editor.org/info/rfc7515>.
[RFC7797]
Jones, M., "JSON Web Signature (JWS) Unencoded Payload Option", RFC 7797, DOI 10.17487/RFC7797, , <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, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8259]
Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, , <https://www.rfc-editor.org/info/rfc8259>.
[RFC8693]
Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J., and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693, DOI 10.17487/RFC8693, , <https://www.rfc-editor.org/info/rfc8693>.
[RFC8705]
Campbell, B., Bradley, J., Sakimura, N., and T. Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens", RFC 8705, DOI 10.17487/RFC8705, , <https://www.rfc-editor.org/info/rfc8705>.

Appendix A. Document History

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.

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.

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.

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.

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"
    }
}

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.

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.

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.

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.

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.

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.

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

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

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

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

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

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": {
            "method": "redirect",
            "uri": "https://client.example.net/return?state=123455",
            "nonce": "LKLTI25DK82FX4T4QFZC"
        }
    }
}

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

From here, the protocol continues as above.

Appendix E. JSON Structures and Polymorphism

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

In JSON, the named members of an object have no type associated with them, and any data type can be used as the value for any member. In practice, each member has a semantic type that needs to make sense to the parties creating and consuming the object. Within this protocol, each object member is defined in terms of its semantic content, and this semantic content might have expressions in different concrete data types for different specific purposes. Since each object member has exactly one value in JSON, each data type for an object member field is naturally mutually exclusive with other data types within a single JSON object.

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

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

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

Extensions to this specification can use different data types for defined fields, but

Author's Address

Justin Richer (editor)
Bespoke Engineering