IETF · May 2023
RFC 9396
T. Lodderstedt, J. Richer, B. Campbell
An agent that needs 'create a draft invoice for vendor X under $500' cannot express that in scope=invoices.write. RAR is the OAuth-native answer; AAuth R3 is the agent-native answer.
At a glance
Actors
01
An agent that needs 'create a draft invoice for vendor X under $500' cannot say that with scope=invoices.write. RFC 9396 adds authorization_details: a JSON array of typed objects (locations, actions, datatypes, identifier, privileges, …).
AAuth R3 is the cousin that uses vocabularies agents already speak. Inside vanilla OAuth (including MCP if the AS supports it), RAR is the structured-scope tool.
02
The AS must understand the type URIs. The RS must enforce the same types. A client that invents fields the RS ignores has a false sense of constraint. Users must be shown a rendering they can actually decide on — otherwise RAR is theatre.
03
authorization_details on authorize and token requests (and in JWT access tokens). Each object has a required type plus type-specific fields. Combine with PAR because the payload is large. A 2026 WG draft (draft-ietf-oauth-rar-metadata-remediation) works on metadata and error remediation.
04
Flow 1
Client builds authorization_details (your type URI, actions, locations, limits).
Pushes via PAR, user consents to the rendered request.
Access token carries the granted details (RFC 9068 may include them).
RS authorizes the specific call against those details, not just a scope string.
05
Authorization granularity. Complements scopes. Does not identify the user or the agent instance.
06
Usual transport.
RS can read authorization_details without introspection.
Agent-native analogue on AAuth, not wire-compatible.
Often combined in high-value APIs.
07
Granting structured details the RS ignores collapses back to a coarse token.
Define a type URI you control. Do not reuse someone else's type with different fields.
08
RFC 9396, May 2023. Stable. https://www.rfc-editor.org/rfc/rfc9396.html
Define a type URI you control. A 2026 WG draft (draft-ietf-oauth-rar-metadata-remediation) works on metadata and error remediation for RAR. AAuth R3 is a cousin idea using vocabularies agents already speak (OpenAPI, MCP, GraphQL).