Internet-Draft AAuth-R3 April 2026
Hardt Expires 4 October 2026 [Page]
Workgroup:
TBD
Internet-Draft:
draft-hardt-aauth-r3-latest
Published:
Intended Status:
Standards Track
Expires:
Author:
D. Hardt
Hellō

AAuth Rich Resource Requests (R3)

Abstract

This document defines AAuth Rich Resource Requests (R3), an extension to the AAuth Protocol ([I-D.hardt-aauth-protocol]) that enables structured, vocabulary-based authorization for resource access. Resources publish R3 documents (content-addressed authorization definitions) and advertise vocabularies describing their operations. Agents request access using those vocabularies. Auth tokens carry granted operations in the same vocabulary format, enabling resources to enforce authorization directly from the token. R3 provides human-displayable context for consent decisions and content-addressed audit provenance via the r3_s256 hash in auth tokens.

Discussion Venues

Note: This section is to be removed before publishing as an RFC.

This document is part of the AAuth specification family. Source for this draft and an issue tracker can be found at https://github.com/dickhardt/AAuth.

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 4 October 2026.

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Table of Contents

1. Introduction

Status: Exploratory Draft

The AAuth Protocol ([I-D.hardt-aauth-protocol]) defines resource tokens as the mechanism by which resources declare what authorization is needed to access them, and scope strings as the primary way to express what operations are available. Scopes are sufficient for simple, well-known access patterns but are limited in three respects:

  1. Human comprehension. Scope strings like calendar:write are not self-describing to users or auth agents making approval decisions.

  2. Machine precision. Scopes do not express which specific operations are being authorized or distinguish operations that need per-call approval.

  3. Audit completeness. Scopes do not identify which specific version of an authorization definition was in effect at the time of approval.

R3 addresses these by introducing:

2. Conventions and Definitions

{::boilerplate bcp14-tagged}

3. Terminology

4. Vocabularies

Resources advertise their supported vocabularies in well-known metadata. Each vocabulary maps to an API description format that agents already know how to discover and parse.

4.1. Resource Metadata Extensions

R3 extends the /.well-known/aauth-resource.json document defined in AAuth Protocol ([I-D.hardt-aauth-protocol]):

{
  "resource": "https://calendar.example.com",
  "resource_token_endpoint": "https://calendar.example.com/aauth/token",
  "r3_vocabularies": {
    "urn:aauth:vocabulary:mcp": "https://calendar.example.com/mcp",
    "urn:aauth:vocabulary:openapi": "https://calendar.example.com/openapi.json"
  }
}

r3_vocabularies (OPTIONAL). A JSON object mapping vocabulary URIs to their discovery endpoints. Keys MUST be vocabulary URIs from the urn:aauth:vocabulary: namespace for standard vocabularies defined in this document, or third-party URI namespaces for proprietary vocabularies. Values are vocabulary-specific discovery endpoints (the MCP server URL, the OpenAPI spec URL, the gRPC reflection endpoint, etc.). A resource MAY advertise multiple vocabularies simultaneously.

4.2. Standard Vocabularies

This document defines seven standard vocabularies. Third parties MAY define additional vocabularies using their own URI namespaces. Each vocabulary defines: the vocabulary URI, the structure of operation requests, how the resource maps operations to R3 documents, and the discovery endpoint.

Standard vocabularies use the urn:aauth:vocabulary: namespace.

4.2.1. MCP Vocabulary (urn:aauth:vocabulary:mcp)

For resources that expose an MCP server. The discovery endpoint is the MCP server URL. Agents discover available tool names via MCP tool discovery.

Each operation entry contains:

  • tool (REQUIRED). The MCP tool name as advertised by the MCP server's tool discovery. 
{
  "vocabulary": "urn:aauth:vocabulary:mcp",
  "operations": [
    { "tool": "create_calendar_event" },
    { "tool": "modify_calendar_event" }
  ]
}

4.2.2. OpenAPI Vocabulary (urn:aauth:vocabulary:openapi)

For resources that expose an OpenAPI-described HTTP API. The discovery endpoint is the OpenAPI specification URL. Agents discover available operations by fetching and parsing the spec.

Each operation entry contains:

  • operationId (REQUIRED). The operationId as defined in the OpenAPI specification. 
{
  "vocabulary": "urn:aauth:vocabulary:openapi",
  "operations": [
    { "operationId": "createEvent" },
    { "operationId": "updateEvent" }
  ]
}

4.2.3. gRPC Vocabulary (urn:aauth:vocabulary:grpc)

For resources that expose a gRPC server. The discovery endpoint is the gRPC server reflection endpoint (supporting grpc.reflection.v1.ServerReflection) or a hosted .proto file URL.

Each operation entry contains:

  • method (REQUIRED). The fully qualified gRPC method name in the form package.ServiceName/MethodName. 
{
  "vocabulary": "urn:aauth:vocabulary:grpc",
  "operations": [
    { "method": "calendar.CalendarService/CreateEvent" },
    { "method": "calendar.CalendarService/UpdateEvent" }
  ]
}

4.2.4. GraphQL Vocabulary (urn:aauth:vocabulary:graphql)

For resources that expose a GraphQL API. The discovery endpoint is the GraphQL endpoint. Agents discover available operations via GraphQL introspection (__schema query).

Each operation entry contains:

  • operation (REQUIRED). The GraphQL operation name. MUST be a named query, mutation, or subscription.
  • type (REQUIRED). One of query, mutation, or subscription. 
{
  "vocabulary": "urn:aauth:vocabulary:graphql",
  "operations": [
    { "operation": "CreateCalendarEvent", "type": "mutation" },
    { "operation": "GetCalendarEvents", "type": "query" }
  ]
}

4.2.5. AsyncAPI Vocabulary (urn:aauth:vocabulary:asyncapi)

For resources that expose an event-driven interface described by AsyncAPI. The discovery endpoint is the AsyncAPI specification URL.

Each operation entry contains:

  • operationId (REQUIRED). The operationId as defined in the AsyncAPI specification.
  • action (REQUIRED). One of send or receive. 
{
  "vocabulary": "urn:aauth:vocabulary:asyncapi",
  "operations": [
    { "operationId": "publishCalendarUpdate", "action": "send" },
    { "operationId": "receiveCalendarEvent", "action": "receive" }
  ]
}

4.2.6. WSDL Vocabulary (urn:aauth:vocabulary:wsdl)

For resources that expose a SOAP/WSDL-described web service. The discovery endpoint is the WSDL document URL.

Each operation entry contains:

  • operation (REQUIRED). The operation name as defined in the WSDL portType or binding.
  • service (OPTIONAL). The WSDL service name, for disambiguation when multiple services expose the same operation name. 
{
  "vocabulary": "urn:aauth:vocabulary:wsdl",
  "operations": [
    { "operation": "CreateCalendarEvent", "service": "CalendarService" }
  ]
}

4.2.7. OData Vocabulary (urn:aauth:vocabulary:odata)

For resources that expose an OData service. The discovery endpoint is the OData service root URL. Agents discover entity sets, functions, and actions via the $metadata document.

Each operation entry contains:

  • operation (REQUIRED). An entity set name, a bound function (EntitySet/FunctionName), or a bound action (EntitySet/ActionName).
  • methods (OPTIONAL). An array of HTTP methods for entity set CRUD (e.g., ["GET", "POST"]). Omitted for bound functions and actions. 
{
  "vocabulary": "urn:aauth:vocabulary:odata",
  "operations": [
    { "operation": "Events", "methods": ["GET", "POST", "PATCH"] },
    { "operation": "Events/SendCancellation" }
  ]
}

5. Resource Token Endpoint

When an agent wants to acquire a resource token proactively, before making an API call rather than waiting for a 401, it calls the resource_token_endpoint with an r3_operations parameter describing what it intends to do in the resource's vocabulary.

5.1. Request 

POST /aauth/token HTTP/1.1
Host: calendar.example.com
Content-Type: application/json
Signature-Input: sig=("@method" "@authority" "@path" "signature-key");created=1741824000
Signature: sig=:...signature bytes...:
Signature-Key: sig=jwt;jwt="eyJhbGc..."

{
  "r3_operations": {
    "vocabulary": "urn:aauth:vocabulary:openapi",
    "operations": [
      { "operationId": "createEvent" },
      { "operationId": "updateEvent" }
    ]
  }
}

r3_operations (REQUIRED). An object containing:

  • vocabulary (REQUIRED). A URI identifying the vocabulary. MUST be supported by the resource as advertised in r3_vocabularies.
  • operations (REQUIRED). An array of operation requests. Structure is vocabulary-specific; see {{mcp-vocabulary}} through {{odata-vocabulary}}.

5.2. Response

The resource maps the declared operations to an appropriate R3 document and returns a signed resource token:

{
  "resource_token": "eyJhbGciOiJFUzI1NiJ9..."
}

The resource token contains r3_uri and r3_s256 identifying the R3 document that covers the requested operations. The resource's internal mapping from operations to R3 documents is opaque to the agent.

6. R3 Document

An R3 document is a JSON object published by the resource at a URI. It describes the authorization semantics for a class of access: what operations are covered (in vocabulary format), what the access means in human terms, and what consequences it carries.

The document MUST be served over HTTPS. The resource MUST require a valid HTTP Message Signature on requests to R3 document URIs, and MUST reject requests that are not signed by the resource's AS. Agents cannot fetch R3 documents.

{
  "type": "urn:example:calendar:write",
  "version": "2",
  "vocabulary": "urn:aauth:vocabulary:mcp",
  "operations": [
    { "tool": "create_calendar_event" },
    { "tool": "modify_calendar_event" }
  ],
  "display": {
    "summary": "Create and modify events on your work calendar",
    "implications": "Meetings can be scheduled or rescheduled. Existing events can be modified.",
    "data_accessed": "Event titles, times, attendees, and descriptions in the work calendar",
    "irreversible": "Sent meeting invitations cannot be unsent"
  }
}

6.1. Fields

type (REQUIRED). A URI identifying the class of authorization. SHOULD be a namespaced URI under the resource's authority.

version (RECOMMENDED). A string identifying the version of this authorization type definition. The combination of URI + SHA-256 hash provides content-addressing independent of this field; version is for human readability.

vocabulary (REQUIRED). The vocabulary URI identifying how operations are expressed. MUST match one of the vocabularies the resource advertises in r3_vocabularies.

operations (REQUIRED). An array of operations covered by this R3 document, using the vocabulary-specific structure defined in {{mcp-vocabulary}} through {{odata-vocabulary}}. This is the same format used in the agent's r3_operations request and in the auth token's r3_granted and r3_conditional claims.

display (RECOMMENDED). Human-readable descriptions of the consequences of granting this access. The resource describes what it does, not what the agent intends:

  • summary (REQUIRED if display present). A short plain-language description suitable for a consent UI or auth agent.
  • implications (OPTIONAL). Side effects of granting this access: emails sent, records modified, costs incurred.
  • data_accessed (OPTIONAL). What data becomes visible to the caller.
  • irreversible (OPTIONAL). Plain-language description of actions that cannot be undone.

6.2. Content Addressing

The R3 hash (r3_s256) is computed as the SHA-256 hash of the canonical JSON serialization ([RFC8785]) of the R3 document, base64url-encoded without padding.

The r3_s256 hash is the document's identity, not the URI. The AS caches documents by hash. If a resource updates the document at the same URI, existing auth tokens still reference the previous hash (which the AS has cached). New resource tokens reference the new hash. This enables:

  • Infinite caching by the AS. A document that verifies against its hash need never be re-fetched.
  • Permanent audit records. An auth token carrying r3_s256 identifies the exact authorization semantics that were approved, regardless of subsequent changes at the same URI.

6.3. Resource Token Extensions

R3 extends the resource token defined in AAuth Protocol ([I-D.hardt-aauth-protocol]) (a JWT with typ: resource+jwt) with two additional payload claims. When a resource includes R3 information, it MUST include both.

Base claims (from AAuth Protocol): - iss: Resource URL - dwk: aauth-resource.json - aud: Auth server URL - jti: Unique token identifier - agent: Agent identifier - agent_jkt: JWK Thumbprint of the agent's signing key - iat: Issued at timestamp - exp: Expiration timestamp - scope: Requested scopes (optional)

R3 extension claims: - r3_uri (REQUIRED for R3): The URI where the AS can fetch the R3 document. The AS authenticates itself using an HTTP Message Signature. - r3_s256 (REQUIRED for R3): The SHA-256 hash of the R3 document at r3_uri, base64url-encoded without padding.

{
  "typ": "resource+jwt",
  "alg": "ES256",
  "kid": "resource-key-1"
}


{
  "iss": "https://calendar.example.com",
  "dwk": "aauth-resource.json",
  "aud": "https://as.example.com",
  "jti": "rt-8f3a2b",
  "agent": "assistant@agent.example",
  "agent_jkt": "NzbLsXh8uDCcd-6MNwXF4W_7noWXFZAfHkxZsRGC9Xs",
  "r3_uri": "https://calendar.example.com/r3/a1b2c3d4",
  "r3_s256": "aBcDeFgHiJkLmNoPqRsTuVwXyZ0123456789abcd",
  "iat": 1741824000,
  "exp": 1741824300
}

Resource tokens MAY include both scope (as defined in AAuth Protocol ([I-D.hardt-aauth-protocol])) and R3 claims. When both are present, the AS MUST enforce both independently.

7. AS Processing

When the AS receives a resource token containing r3_uri and r3_s256, it MUST:

  1. Validate the resource token signature per AAuth Protocol ([I-D.hardt-aauth-protocol]).
  2. Fetch the R3 document at r3_uri. The AS MAY use a cached copy if the cache entry was stored with the same r3_s256 value.
  3. Compute the SHA-256 hash of the fetched document using canonical JSON serialization ([RFC8785]) and compare it to r3_s256. If the hashes do not match, the AS MUST reject the resource token.
  4. Record r3_uri and r3_s256 in its audit log alongside the token issuance event, the agent identifier, and the timestamp.
  5. Use the display section when presenting the authorization request to a human approver or auth agent, and the operations section for policy evaluation.
  6. Include r3_uri, r3_s256, r3_granted, and (if applicable) r3_conditional in the issued auth token.

7.1. Caching

Because R3 documents are content-addressed, the AS SHOULD cache them indefinitely once verified. The cache key is r3_s256. A cache hit on r3_s256 MUST still verify that the stored document produces the same hash. The URI need not be re-fetched.

8. Auth Token Extensions

R3 extends the auth token defined in AAuth Protocol ([I-D.hardt-aauth-protocol]) (a JWT with typ: auth+jwt) with claims for audit provenance and vocabulary-based grants. The resource can enforce authorization directly from these claims.

Base claims (from AAuth Protocol): - iss: Auth server URL - dwk: aauth-issuer.json - aud: Resource URL - jti: Unique token identifier - agent: Agent identifier - cnf: Confirmation claim with jwk containing the agent's public key - iat: Issued at timestamp - exp: Expiration timestamp - sub: User identifier (conditional) - scope: Authorized scopes (conditional)

R3 extension claims: - r3_uri (REQUIRED for R3): The URI of the R3 document that was in effect at approval time. - r3_s256 (REQUIRED for R3): The SHA-256 hash of that R3 document. - r3_granted (REQUIRED for R3): Operations the AS fully authorized. The resource serves these immediately. - r3_conditional (OPTIONAL): Operations authorized in principle but requiring per-call approval based on the specific parameters the agent provides.

{
  "typ": "auth+jwt",
  "alg": "ES256",
  "kid": "as-key-1"
}


{
  "iss": "https://as.example.com",
  "dwk": "aauth-issuer.json",
  "aud": "https://calendar.example.com",
  "jti": "at-9d4c1e",
  "agent": "assistant@agent.example",
  "sub": "user:alice@example.com",
  "cnf": { "jwk": { "kty": "OKP", "crv": "Ed25519", "x": "NzbLsXh8uDCcd..." } },
  "r3_uri": "https://calendar.example.com/r3/a1b2c3d4",
  "r3_s256": "aBcDeFgHiJkLmNoPqRsTuVwXyZ0123456789abcd",
  "r3_granted": {
    "vocabulary": "urn:aauth:vocabulary:mcp",
    "operations": [
      { "tool": "list_calendar_events" },
      { "tool": "modify_calendar_event" }
    ]
  },
  "r3_conditional": {
    "vocabulary": "urn:aauth:vocabulary:mcp",
    "operations": [
      { "tool": "create_calendar_event" }
    ]
  },
  "iat": 1741824000,
  "exp": 1741824900
}

r3_uri and r3_s256 provide audit provenance: a permanent, verifiable record of which R3 document was in effect at approval time. The AS can verify the R3 document by fetching r3_uri and checking r3_s256.

r3_granted and r3_conditional use the same vocabulary-specific operation format as the R3 document's operations field and the agent's r3_operations request:

The distinction: r3_granted operations are fully authorized and the resource serves them. r3_conditional operations require the resource to challenge when the agent actually calls, including the specific parameters from the agent's API request in the resource token. The AS then evaluates those concrete parameters before issuing a per-call auth token.

8.1. Resource Enforcement

The resource matches each incoming API call against the auth token claims:

  1. Match in r3_granted: serve the request.
  2. Match in r3_conditional: return AAuth-Requirement with a resource token containing the actual parameters the agent provided. The AS evaluates the specific call.
  3. No match: reject the request.

No token introspection or R3 document fetch is needed at enforcement time. The resource uses the vocabulary it already understands.

When r3_operations was not used (the agent received the resource token via a 401 rather than the resource token endpoint), the AS populates r3_granted and r3_conditional based on the operations defined in the R3 document and its own policy. The AS decides which operations to grant outright and which to make conditional.

9. Security Considerations

9.1. R3 Document Access Restriction

The AS MUST authenticate itself when fetching r3_uri using an HTTP Message Signature as defined in AAuth Headers ([I-D.hardt-aauth-headers]). The resource MUST reject requests not signed by its AS.

This prevents agents from fetching R3 documents by following the r3_uri they carry in the resource token. Since a resource has exactly one AS, the resource only needs to recognize signatures from that AS. The agent opacity property (agents carry the hash of a document they cannot read) depends on this restriction.

9.2. Hash Verification

The AS MUST verify r3_s256 against the fetched document before using it. Failure to verify allows a resource to serve different content than what was hashed in the resource token.

9.3. Audit Log Integrity

The AS MUST write audit log entries atomically with token issuance. An auth token issued without a corresponding audit log entry creates an undetectable gap in the observability record. Implementations SHOULD use transactional writes or equivalent mechanisms.

9.4. Operation Validation

For all vocabularies, the resource MUST validate declared operations against its authoritative definition (MCP tool list, OpenAPI spec, .proto file, GraphQL schema, AsyncAPI spec, WSDL document, or OData $metadata) before issuing a resource token.

9.5. Grant Enforcement

Resources MUST enforce r3_granted and r3_conditional claims in auth tokens. Operations in r3_granted define fully authorized access. Operations in r3_conditional MUST trigger an AAuth-Requirement before being served. The resource MUST reject API calls that do not match an operation in either claim.

10. IANA Considerations

10.1. JWT Claims Registration

This document requests registration of the following JWT claims in the IANA JSON Web Token Claims registry:

Table 1
Claim Description Reference
r3_uri R3 document URI This document
r3_s256 R3 document SHA-256 hash This document
r3_granted Fully authorized operations in vocabulary format This document
r3_conditional Conditionally authorized operations requiring per-call approval This document

10.2. R3 Vocabulary Registry

This specification establishes the AAuth R3 Vocabulary Registry. The initial contents are:

Table 2
Vocabulary URI Interface Type Reference
urn:aauth:vocabulary:mcp MCP server This document
urn:aauth:vocabulary:openapi HTTP/REST This document
urn:aauth:vocabulary:grpc gRPC This document
urn:aauth:vocabulary:graphql GraphQL This document
urn:aauth:vocabulary:asyncapi Event-driven This document
urn:aauth:vocabulary:wsdl SOAP/WSDL This document
urn:aauth:vocabulary:odata OData This document

New values may be registered following the Specification Required policy ([RFC8126]).

11. Implementation Status

Note: This section is to be removed before publishing as an RFC.

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs.

There are currently no known implementations.

12. Document History

Note: This section is to be removed before publishing as an RFC.

13. Acknowledgments

The author would like to thank reviewers for their feedback.

14. References

14.1. Normative References

[I-D.hardt-aauth-headers]
Hardt, D., "HTTP AAuth Headers", , <https://github.com/dickhardt/AAuth>.
[I-D.hardt-aauth-protocol]
Hardt, D., "AAuth Protocol", , <https://github.com/dickhardt/AAuth>.
[RFC8126]
Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, , <https://www.rfc-editor.org/info/rfc8126>.
[RFC8785]
Rundgren, A., Jordan, B., and S. Erdtman, "JSON Canonicalization Scheme (JCS)", RFC 8785, DOI 10.17487/RFC8785, , <https://www.rfc-editor.org/info/rfc8785>.

14.2. Informative References

[RFC7942]
Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, , <https://www.rfc-editor.org/info/rfc7942>.
[RFC9396]
Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0 Rich Authorization Requests", RFC 9396, DOI 10.17487/RFC9396, , <https://www.rfc-editor.org/info/rfc9396>.

Appendix A. Design Rationale

A.1. Why Not RAR

OAuth 2.0 Rich Authorization Requests ([RFC9396]) defines authorization_details as a structured extension to authorization requests. RAR is a natural reference point for this work. R3 deliberately does not use or profile RAR for the following reasons:

Directionality. RAR is client-declared: the agent constructs authorization_details and sends it to the AS. The agent defines what it wants. R3 is resource-declared: the resource defines what access it provides and signs that definition. The agent cannot modify or reframe it. This is the opposite directionality, and the security properties depend on it.

Agent opacity. In R3, the R3 document is fetched by the AS directly from the resource, restricted to AS-only access. The agent carries a hash of a document it cannot read. RAR has no equivalent because the client constructs the authorization details and necessarily knows their content.

Content addressing. R3 uses a content-addressed URI plus SHA-256 hash to pin the exact authorization semantics in effect at approval time. An auth token carrying r3_uri and r3_s256 is a permanent, verifiable record. RAR carries no equivalent versioning or integrity guarantee.

Audit trail. The AS records r3_uri in its audit log, creating a durable reference to the exact R3 document version. This is not possible with RAR's inline authorization_details structure.

RAR and R3 are complementary. RAR remains appropriate for client-declared authorization detail. R3 addresses the resource-declared case that RAR was not designed for.

Appendix B. Vocabulary Summary

Table 3
Vocabulary URI Interface Type Operation Identifier Discovery Mechanism
urn:aauth:vocabulary:mcp MCP server Tool name MCP tool discovery
urn:aauth:vocabulary:openapi HTTP/REST operationId OpenAPI spec URL
urn:aauth:vocabulary:grpc gRPC package.Service/Method Server reflection or .proto URL
urn:aauth:vocabulary:graphql GraphQL Operation name GraphQL introspection
urn:aauth:vocabulary:asyncapi Event-driven operationId AsyncAPI spec URL
urn:aauth:vocabulary:wsdl SOAP/WSDL Operation name WSDL document URL
urn:aauth:vocabulary:odata OData Entity set or bound operation $metadata URL

Appendix C. Comparison with RAR

Table 4
Property RAR ([RFC9396]) R3
Who declares Client (agent) Resource
Direction Client -> AS Resource -> AS (via agent carrier)
Agent visibility Agent constructs the detail Agent carries opaque token
Versioning None Content-addressed URI + hash
Audit trail Inline in request r3_uri recorded by AS
Human display Not specified display section in R3 document
Irreversibility signal Not specified display.irreversible field

Author's Address

Dick Hardt
Hellō