]> Raiffeisen Bank International

yaron.zehavi@rbinternational.com

Security Web Authorization Protocol RAR Step-up oauth OAuth 2.0 Rich Authorization Requests (RAR), as defined in , enables clients to request fine-grained authorization using structured JSON objects. While RAR standardizes the exchange and handling of authorization details, it does not define a mechanism for clients to discover how to construct valid authorization details types. This document defines a machine-readable metadata structure for advertising authorization details type documentation and JSON Schema definitions via OAuth Authorization Server Metadata and OAuth Resource Server Metadata . In addition, this document defines a new OAuth error code, insufficient_authorization_details, enabling resource servers to return actionable authorization details objects to clients. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Web Authorization Protocol Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction OAuth 2.0 Rich Authorization Requests (RAR) allows OAuth clients to request structured, fine-grained authorization, beyond the coarse-grained access offered by simple scopes. This has enabled advanced authorization models across domains, such as open banking & API marketplaces, and is well positioned for authorizing AI agents to perform state-changing actions. However, RAR does not specify how a client discovers the structure of supported authorization_detail types and how to construct syntactically valid authorization details. As a result, clients must rely on out-of-band documentation or static ecosystem profiles, limiting interoperability and preventing dynamic client behavior. This document addresses this gap by defining:

• A metadata structure for authorization details types, containing both human-readable documentation as well as embedded JSON Schema definitions.
• Discovery through Authorization Server Metadata , as well as via OAuth 2.0 Protected Resource Metadata .
• A standardized error signaling mechanism, allowing resource servers to return an authorization details object, to be included in a new Auth request, in order to accomplish a specific request.

It is up to implementers to decide if their clients MUST learn to construct valid authorization details objects, and if so whether authorization details types metadata should be provided by authorization servers, resource servers or both. This document also outlines a solution pattern relieving clients from having to learn how to construct valid authorization details objects, instead providing clients the required authorization_details objects in resource servers' error responses. Clients then include the provided authorization details objects in subsequent OAuth requests. This latter option is especially useful, as it enables resource servers to include ephemeral, interaction-specific details in the authorization details object, which are part of the resource domain, such as a risk score, risk profile or an internal interaction identifier.

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here.

Protocol Overview There are two main proposed flows, either of them or both may be offered in parallel:

• Client learns to construct valid authorization details objects from authorization details types metadata provided by authorization servers, resource servers or both.
• Client obtains authorization details object from resource server's error response, providing an actionable authorization details object, whose inclusion in subsequent OAuth requests is required to accomplish a specific request.

Client learns to construct valid authorization details objects from metadata |+------------------+| Starts| | | || Metadata || Flow +-->| Client |<----------------------|| Endpoint || | | (C) Metadata Response |+------------------+| | | : +--------------------+ | | (D) Construct RAR | | Using Metadata | | : +--------------------+ | | (E) Authorization | Authorization | | | Request + RAR | Server | | |---------------------->|+------------------+| | | || Authorization || | |<----------------------|| Endpoint || | | (F) Authorization Code|| || | | : |+------------------+| | | : | | | | (G) Token Request |+------------------+| | |---------------------->|| || | | || Token Endpoint || | |<----------------------|| || | | (H) Access Token |+------------------+| | | : +--------------------+ | | : | | (I) API Call with | | Access Token +--------------------+ | |---------------------->| | | | | Resource Server | | |<----------------------| | | | (J) 200 OK + Resource +--------------------+ | | +----------+ ]]> Figure: Client learns to construct valid authorization details objects from metadata

• (A) The user starts the flow.
• (B-C) The client discovers authorization details type metadata from Authorization Server Metadata , or from resource server Protected Resource Metadata
• (D-E) The client constructs a valid authorization details object and makes an OAuth + RAR request.
• (F) Authorization server returns authorization code.
• (G-H) The client exchanges authorization code for access token.
• (I) The client makes API request with access token.
• (J) Resource server validates access token and returns successful response.

Client obtains authorization details object from resource server's error response | Resource | (A) User +---| | | Server | Starts| | |<----------------------| | Flow +-->| Client | (C) 403 Forbidden +--------------------+ | | WWW-Authenticate | | error="insufficient_authorization_details" | | + authorization_details | | : | | : +--------------------+ | | : | Authorization | | | (D) Authorization | Server | | | Request + RAR |+------------------+| | |---------------------->|| || | | || Authorization || | |<----------------------|| Endpoint || | | (E) Authorization Code|| || | | : |+------------------+| | | : | | | | (G) Token Request |+------------------+| | |---------------------->|| || | | || Token Endpoint || | |<----------------------|| || | | (H) Access Token |+------------------+| | | : +--------------------+ | | : | | : | | (I) Retry API Call +--------------------+ | | with Token | | | |---------------------->| Resource | | | | Server | | |<----------------------| | | | (J) 200 OK + Resource +--------------------+ | | +----------+ ]]> Figure: Client obtains authorization details object from resource server's error response

• (A) The user starts the flow.
• (B) The client calls an API with an access token.
• (C) Resource server returns HTTP 403 forbidden because the access token does not contain required authorization details. Resource server's response includes a WWW-Authenticate header with the authorization details object requiring approval.
• (D) The client uses the obtained authorization details object in a new OAuth + RAR request.
• (E) Authorization server returns authorization code.
• (G-H) The client exchanges authorization code for access token.
• (I) The client makes API request with access token.
• (J) Resource server validates access token and returns successful response.

Authorization Details Type Metadata

Overview This document defines a new metadata attribute, authorization_details_types_metadata, which provides documentation and validation information for authorization details types used with Rich Authorization Requests . The new metadata property MAY be published by OAuth authorization servers using Authorization Server Metadata as well as by Resource Servers using Protected Resource Metadata . Clients MAY use this metadata to dynamically construct valid authorization_details objects. This document also proposes the existing authorization_details_types_supported metadata attributed defined by RAR , be included in Protected Resource Metadata .

Metadata Location The authorization_details_types_metadata attribute may be included in:

• Authorization Server Metadata , to describe authorization details types supported by the authorization server. If present, its keys MUST be a subset of the values listed in authorization_details_types_supported as defined in .
• OAuth 2.0 Protected Resource Metadata , to describe authorization details types accepted by the protecred resource.

Metadata Structure The authorization_details_types_metadata attribute is a JSON object whose keys are authorization details type identifiers. Each value is an object describing a single authorization details type. Attributes definition:

"version":

OPTIONAL. String identifying the version of the authorization details type definition. The value is informational and does not imply semantic version negotiation.

"description":

OPTIONAL. String containing a human-readable description of the authorization details type. Clients MUST NOT rely on this value for authorization or validation decisions.

"documentation_uri":

OPTIONAL. URI referencing external human-readable documentation describing the authorization details type.

"schema":

The schema attribute is a JSON Schema document describing a single authorization detail object. The schema MUST validate a single authorization detail object and MUST constrain the type attribute to the authorization detail type identifier. This attribute is REQUIRED unless schema_uri is specified. If this attribute is present, schema_uri MUST NOT be present.

"schema_uri":

The schema_uri attribute is an absolute URI, as defined by RFC 3986 , referencing a JSON Schema document describing a single authorization details object. The referenced schema MUST satisfy the same requirements as the schema attribute. This attribute is REQUIRED unless schema is specified. If this attribute is present, schema MUST NOT be present.

"examples":

OPTIONAL. An array of example authorization details objects. Examples are non-normative.

Metadata Examples

Example RAR Metadata: Payment Initiation

Resource Server Error Signaling with insufficient_authorization_details

Overview This document defines a new OAuth error code, insufficient_authorization_details, for use when access is denied due to missing or insufficient authorization details.

Error Definition The error MUST be conveyed using the WWW-Authenticate header and MUST include an authorization_details parameter.

authorization_details Error Parameter The parameter MUST contain a JSON object or array, representing the required authorization details, whose inclusion in a subsequent OAuth request is required to satisfy the resource server's requirements for this specific request. The value MUST be base64url-encoded.

Processing Rules

Client Processing Rules

• Fetch authorization_details_types_metadata from the authorization or resource server's metadata endpoints.
• Locate schema or retrieve schema_uri.
• Construct authorization details conforming to the schema.
• If resource server returns error insufficient_authorization_details, use provided authorization_details in subsequent OAuth request, then provide the obtained token to resource server.

Authorization Server Processing Rules

• Advertise authorization_details_types_metadata in metadata.
• Validate each authorization detail against schema.
• Enforce additional semantic checks.
• Reject missing or invalid details with standard OAuth error semantics.

Resource Server Processing Rules

• Advertise authorization_details_types_metadata.
• Verify tokens against required authorization details.
• If insufficient, return HTTP 403 with WWW-Authenticate: Bearer error="insufficient_authorization_details".
• Do not reveal additional sensitive information.

Security Considerations

IANA Considerations

OAuth 2.0 Bearer Token Error Registry

Error Code	Description
insufficient_authorization_details	The request is missing required authorization details or the provided authorization details are insufficient. The resource server SHOULD include the required authorization_details

OAuth Metadata Attribute Registration The metadata attribute authorization_details_types_metadata is defined for OAuth authorization and resource server metadata, as a JSON object mapping authorization details types to documentation, schema, and examples.

Normative References A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] This specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 authorization server, including its endpoint locations and authorization server capabilities. This document specifies a new parameter authorization_details that is used to carry fine-grained authorization data in OAuth messages. This specification defines a metadata format that an OAuth 2.0 client or authorization server can use to obtain the information needed to interact with an OAuth 2.0 protected resource. IANA In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.

Examples This section provides non-normative examples of how this specification may be used to support specific use cases.

Payment initiation with RAR error signaling

Client initiates API request Client uses access token obtained at login to call payment initiation API

Resource server signals insufficient_authorization_details Resource server requires payment approval and responds with: The base64 encoded authorization_details decodes to: Note the resource server has added the ephemeral attributes: interactionId, riskProfile.

Client initiates OAuth flow using the provided authorization_details object After user approves the request, client obtains single-use access token representing the approved payment

Client re-attempts API request

Resource server authorizes the request

Document History -00

• Document creation

Acknowledgments