Web Authorization Protocol D. Liu Internet-Draft H. Zhu Intended status: Standards Track Alibaba Group Expires: 25 December 2026 S. Krishnan Cisco A. Parecki Okta 23 June 2026 Authorization Evidence and Audit Trail for OAuth 2.0 Access Tokens draft-liu-oauth-authorization-evidence-01 Abstract This specification defines an authorization details type for including authorization evidence and audit trail information in OAuth 2.0 access tokens using the Rich Authorization Requests (RAR) framework. When an Authorization Server processes user consent, it enriches the authorization details with cryptographic proof of user confirmation, supporting accountability, compliance, and dispute resolution in scenarios where autonomous agents act on behalf of users. 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 25 December 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Liu, et al. Expires 25 December 2026 [Page 1] Internet-Draft OAuth Authorization Evidence June 2026 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Relationship to Rich Authorization Requests . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. The authorization_evidence Authorization Details Type . . . . 5 3.1. Type Definition . . . . . . . . . . . . . . . . . . . . . 5 3.2. Client Request . . . . . . . . . . . . . . . . . . . . . 5 3.3. Enriched Response . . . . . . . . . . . . . . . . . . . . 5 3.4. Evidence Object Structure . . . . . . . . . . . . . . . . 6 3.5. Field Definitions . . . . . . . . . . . . . . . . . . . . 7 3.5.1. user_confirmation Object . . . . . . . . . . . . . . 7 3.6. AS Signature . . . . . . . . . . . . . . . . . . . . . . 8 4. The audit_trail Sub-object . . . . . . . . . . . . . . . . . 9 4.1. Structure . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2. Field Definitions . . . . . . . . . . . . . . . . . . . . 10 4.3. Semantic Expansion Levels . . . . . . . . . . . . . . . . 11 5. Audit Trail Purposes . . . . . . . . . . . . . . . . . . . . 12 6. Authorization Server Processing . . . . . . . . . . . . . . . 12 6.1. Evidence Collection from User Interaction . . . . . . . . 12 6.1.1. General Consent-to-Evidence Pattern . . . . . . . . . 12 6.1.2. Consent UI to Evidence Field Mapping . . . . . . . . 13 6.1.3. Example: JWT Grant Interaction Response Flow . . . . 14 6.1.4. Applicability to Other Flows . . . . . . . . . . . . 15 6.2. Evidence Generation . . . . . . . . . . . . . . . . . . . 16 7. Resource Server Processing . . . . . . . . . . . . . . . . . 16 7.1. Evidence Verification . . . . . . . . . . . . . . . . . . 16 7.2. Audit Logging . . . . . . . . . . . . . . . . . . . . . . 17 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8.1. Signature Verification . . . . . . . . . . . . . . . . . 17 8.2. Evidence Tampering and Trust in the AS . . . . . . . . . 17 8.3. Replay Attacks . . . . . . . . . . . . . . . . . . . . . 18 8.4. Token-Evidence Binding . . . . . . . . . . . . . . . . . 18 8.5. Cross-Domain Evidence Verification . . . . . . . . . . . 19 8.6. Privacy Considerations . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9.1. OAuth Authorization Details Type Registration . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 Liu, et al. Expires 25 December 2026 [Page 2] Internet-Draft OAuth Authorization Evidence June 2026 10.1. Normative References . . . . . . . . . . . . . . . . . . 19 10.2. Informative References . . . . . . . . . . . . . . . . . 20 Appendix A. Complete Example . . . . . . . . . . . . . . . . . . 21 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 1. Introduction In traditional OAuth 2.0 [RFC6749] flows, the Authorization Server records user consent internally, but this information is not typically conveyed to Resource Servers or included in access tokens. For many use cases, this is sufficient. However, emerging scenarios, particularly those involving AI agents acting autonomously on behalf of users, require stronger guarantees about user intent and consent. This specification addresses the need for: * Verifiable consent: Cryptographic proof that a user explicitly authorized a specific operation; * Audit trails: Traceable records linking user intent to system actions; * Dispute resolution: Evidence that can be examined if questions arise about what was authorized; * Regulatory compliance: Documentation required by applicable regulations. This specification defines an authorization details type that leverages the Rich Authorization Requests (RAR) [RFC9396] framework to convey authorization evidence. When a client includes an authorization_evidence authorization details object in its request, the Authorization Server enriches it during the consent process with cryptographic proof of user confirmation. Unless otherwise noted, all data types and serialization rules follow the JSON data interchange format as defined in [RFC8259]. 1.1. Requirements Language 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. Liu, et al. Expires 25 December 2026 [Page 3] Internet-Draft OAuth Authorization Evidence June 2026 1.2. Relationship to Rich Authorization Requests This specification builds on the Rich Authorization Requests (RAR) framework [RFC9396]. In RAR, clients include authorization_details in authorization requests to convey fine-grained authorization data. RAR Section 7.1 defines an "Enriched Response" mechanism where the Authorization Server dynamically populates fields in the authorization_details based on user consent decisions or policy rules. The authorization_evidence type defined in this specification follows this enriched response pattern: 1. The client includes an authorization_evidence authorization details object in its request, typically with minimal or placeholder fields indicating that evidence is requested. 2. During the consent interaction, the AS presents the requested operation to the user and captures the user's confirmation action. 3. The AS enriches the authorization_evidence object with the complete evidence record, including user_confirmation details and the AS's cryptographic signature. 4. The enriched authorization details is included in the token response and bound to the issued access token. This approach ensures that authorization evidence is structured as a first-class authorization detail rather than a standalone JWT claim, enabling consistent handling across OAuth flows and composability with other authorization details types. 2. Terminology User Confirmation: An explicit action by the user (e.g., clicking "Allow") to approve an authorization request. Displayed Content: The human-readable description of the operation shown to the user during the consent flow. Evidence: A cryptographically signed record of user confirmation, including what was displayed and how the user responded. Audit Trail: Metadata that enables tracing from user intent through system interpretation to final authorized action. Semantic Expansion: The process of translating user intent (e.g., Liu, et al. Expires 25 December 2026 [Page 4] Internet-Draft OAuth Authorization Evidence June 2026 natural language) into concrete system operations. 3. The authorization_evidence Authorization Details Type The authorization_evidence authorization details type contains a record of the user's confirmation action during the authorization process. Following the RAR enriched response pattern ([RFC9396] Section 7.1), the client requests this type and the AS enriches it with the complete evidence record. 3.1. Type Definition Type Identifier: authorization_evidence Usage: authorization_details in authorization requests and token responses 3.2. Client Request A client requests authorization evidence by including an authorization_evidence authorization details object in its authorization request. The client typically includes minimal fields, indicating that evidence is requested: { "authorization_details": [ { "type": "authorization_evidence" } ] } Figure 1 The client MAY include optional fields to indicate preferences, such as specific audit trail requirements. However, the AS has final authority over the evidence content based on the actual consent interaction. 3.3. Enriched Response After the user completes the consent interaction, the AS enriches the authorization_evidence object with the complete evidence record. The enriched authorization details is included in the token response: Liu, et al. Expires 25 December 2026 [Page 5] Internet-Draft OAuth Authorization Evidence June 2026 { "authorization_details": [ { "type": "authorization_evidence", "evidence": { "id": "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6", "user_confirmation": { "displayed_content": "Add items under $50 to cart", "user_action": "confirmed_via_button_click", "timestamp": 1731320595 }, "as_signature": "eyJhbGciOiJFUzI1NiJ9..MEUCIQDx...", "audit_trail": { "semantic_expansion_level": "medium", "proposal_ref": "urn:uuid:proposal-xyz" } } } ] } Figure 2 3.4. Evidence Object Structure The evidence object within the authorization_evidence authorization details type contains the following fields: { "evidence": { "id": "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6", "user_confirmation": { "displayed_content": "Add items under $50 to cart", "user_action": "confirmed_via_button_click", "timestamp": 1731320595 }, "as_signature": "eyJhbGciOiJFUzI1NiJ9..MEUCIQDx..." } } Figure 3 Liu, et al. Expires 25 December 2026 [Page 6] Internet-Draft OAuth Authorization Evidence June 2026 3.5. Field Definitions +===================+======+===========+==========================+ | Field |Type |Requirement| Description | +===================+======+===========+==========================+ | id |string|REQUIRED | Unique identifier for | | | | | this evidence record. | | | | | The value MUST use a URI | | | | | or URN format with at | | | | | least 128 bits of | | | | | collision resistance. | | | | | UUID URNs (e.g., | | | | | "urn:uuid:f81d4fae-7dec- | | | | | 11d0-a765-00a0c91e6bf6") | | | | | are RECOMMENDED. | +-------------------+------+-----------+--------------------------+ | user_confirmation |object|REQUIRED | Details of the user's | | | | | confirmation action. | +-------------------+------+-----------+--------------------------+ | as_signature |string|REQUIRED | AS signature over the | | | | | confirmation record. | +-------------------+------+-----------+--------------------------+ Table 1: Evidence Object Fields 3.5.1. user_confirmation Object +=================+===========+===========+=========================+ |Field |Type |Requirement| Description | +=================+===========+===========+=========================+ |displayed_content|string |REQUIRED | The text shown to user | | | | | for confirmation. | +-----------------+-----------+-----------+-------------------------+ |user_action |string |REQUIRED | How the user confirmed | | | | | the operation. The | | | | | value is a free-form | | | | | string, but | | | | | implementations SHOULD | | | | | use values from the | | | | | following set for | | | | | interoperability: | | | | | button_click, | | | | | biometric_confirmation, | | | | | pin_entry, | | | | | voice_confirmation, | | | | | hardware_key, | | | | | implicit_consent. | | | | | Custom values MAY be | Liu, et al. Expires 25 December 2026 [Page 7] Internet-Draft OAuth Authorization Evidence June 2026 | | | | used for deployment- | | | | | specific confirmation | | | | | mechanisms. | +-----------------+-----------+-----------+-------------------------+ |timestamp |NumericDate|REQUIRED | When the confirmation | | | | | occurred. | +-----------------+-----------+-----------+-------------------------+ Table 2: user_confirmation Fields 3.6. AS Signature The as_signature field contains a cryptographic signature from the Authorization Server over the evidence record. This signature: * Proves the AS witnessed the user's consent; * Ensures the evidence has not been tampered with; * Provides strong evidence of user consent for dispute resolution (subject to trust in the AS, as discussed in Section 8). The signature MUST be computed over the following fields of the evidence object: * id * user_confirmation (entire object) The as_signature field itself MUST be excluded from the signature computation. The signature format MUST be a detached JWS [RFC7515] in Compact Serialization using the AS's signing key. In detached Compact Serialization (see RFC 7515 Appendix F), the payload portion is omitted, resulting in the format "header..signature". The signature input is constructed using the following deterministic algorithm: 1. Create a new JSON object containing only the id and user_confirmation fields copied from the evidence object. No other fields from the evidence object are included. 2. Apply the JSON Canonicalization Scheme (JCS) as defined in [RFC8785] to the JSON object from the previous step, producing a deterministic byte string. Liu, et al. Expires 25 December 2026 [Page 8] Internet-Draft OAuth Authorization Evidence June 2026 3. Compute a detached JWS (Compact Serialization) over the JCS output from Step 2 using the AS's private signing key. The resulting value (header..signature) is stored in the as_signature field of the evidence object. To verify an as_signature, the verifier reconstructs the JCS input by performing Steps 1 and 2 above on the received evidence object (excluding the as_signature field), then verifies the detached JWS using the AS's public key. Any extension fields present in the evidence object beyond id, user_confirmation, and as_signature MUST NOT be included in the JCS input and therefore are not covered by the signature. Note: In examples throughout this document, the as_signature value is shown in abbreviated form for readability. Actual values MUST use the detached JWS Compact Serialization format described above. The key used to sign the evidence record MAY be the same key used to sign the access token, or it MAY be a separate dedicated key. When a separate key is used, implementations MUST ensure that the evidence signing key is associated with the AS through a verifiable mechanism (e.g., published in the AS's JWKS endpoint as defined in [RFC7517]). Using a dedicated evidence signing key enables independent key rotation without affecting token validation. 4. The audit_trail Sub-object The audit_trail sub-object provides metadata for semantic traceability, enabling analysis of how user intent was interpreted and translated into authorized operations. It is included within the evidence object in the authorization_evidence authorization details type. 4.1. Structure { "audit_trail": { "semantic_expansion_level": "medium", "proposal_ref": "urn:uuid:proposal-xyz" } } Figure 4 Liu, et al. 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Field Definitions +==========================+========+=============+=================+ | Field | Type | Requirement | Description | +==========================+========+=============+=================+ | evidence_ref | string | OPTIONAL | Reference to a | | | | | related | | | | | evidence | | | | | record by ID. | | | | | Can be used to | | | | | link this | | | | | audit trail to | | | | | another | | | | | evidence | | | | | record, such | | | | | as the | | | | | original | | | | | consent in a | | | | | delegation | | | | | chain. | +--------------------------+--------+-------------+-----------------+ | semantic_expansion_level | string | OPTIONAL | Degree of | | | | | interpretation | | | | | applied (none, | | | | | low, medium, | | | | | high). | +--------------------------+--------+-------------+-----------------+ | proposal_ref | URI | OPTIONAL | Reference to | | | | | the original | | | | | authorization | | | | | proposal, the | | | | | agent's | | | | | initial | | | | | request | | | | | describing the | | | | | intended | | | | | operation | | | | | before the AS | | | | | applied policy | | | | | evaluation, | | | | | scope | | | | | reduction, or | | | | | user consent | | | | | modifications. | | | | | The value is | | | | | an opaque URI | | | | | assigned by | | | | | the AS for | Liu, et al. Expires 25 December 2026 [Page 10] Internet-Draft OAuth Authorization Evidence June 2026 | | | | internal | | | | | correlation; | | | | | no protocol | | | | | for retrieving | | | | | the proposal | | | | | content via | | | | | this URI is | | | | | defined by | | | | | this | | | | | specification. | | | | | This enables | | | | | post-hoc | | | | | comparison | | | | | between what | | | | | the agent | | | | | originally | | | | | requested and | | | | | what was | | | | | ultimately | | | | | authorized. | +--------------------------+--------+-------------+-----------------+ Table 3: audit_trail Fields 4.3. Semantic Expansion Levels The semantic_expansion_level field indicates how much the system interpreted or expanded the user's original intent. The following four values form a closed set; implementations MUST NOT use values outside this set: none: No interpretation; user specified exact parameters. Example: User explicitly sets "transfer $100 to account X". low: Minor defaults applied. Example: User says "add to cart" and the system defaults quantity to 1 and selects the user's saved shipping address. medium: Significant interpretation of qualitative terms. Example: User says "buy cheap headphones" and the system maps "cheap" to a price ceiling of $50 and selects a specific product category. high: Substantial expansion from a high-level goal into a multi-step plan. Example: User says "plan my trip to Tokyo" and the agent derives flight search, hotel booking, and itinerary creation as separate authorized operations. Liu, et al. Expires 25 December 2026 [Page 11] Internet-Draft OAuth Authorization Evidence June 2026 5. Audit Trail Purposes The evidence and audit trail objects serve several important purposes: +================+=================================================+ | Purpose | Description | +================+=================================================+ | Intent | Records what the user intended, preventing | | Provenance | disputes about authorization scope. | +----------------+-------------------------------------------------+ | Action | Documents how the system translated intent into | | Interpretation | operations, showing the reasoning process. | +----------------+-------------------------------------------------+ | Semantic | Reveals any expansions or defaults applied, | | Transparency | enabling users to understand what was | | | authorized. | +----------------+-------------------------------------------------+ | User | Provides timestamped proof that the user | | Confirmation | reviewed and approved the operation. | +----------------+-------------------------------------------------+ | Accountability | Enables post-hoc analysis to determine | | Support | responsibility for erroneous transactions. | +----------------+-------------------------------------------------+ Table 4: Purposes of Authorization Evidence 6. Authorization Server Processing 6.1. Evidence Collection from User Interaction The evidence object records the outcome of a user consent interaction. Before the AS can generate a signed evidence record, it must first present a consent interface to the user and capture the user's response. This section describes the general consent-to- evidence pattern and provides a concrete example using the JWT Grant Interaction Response flow. 6.1.1. General Consent-to-Evidence Pattern Regardless of the specific OAuth grant type, evidence collection follows a common pattern: 1. The AS receives an authorization request from a client (which may be acting on behalf of an AI agent). Liu, et al. Expires 25 December 2026 [Page 12] Internet-Draft OAuth Authorization Evidence June 2026 2. The AS determines that user consent is required and presents a consent interface to the user. The consent interface displays a human-readable description of the requested operation (the displayed_content). 3. The user reviews the displayed content and performs a confirmation action (e.g., clicking an "Allow" button, providing biometric input, entering a PIN). 4. The AS captures the interaction details (what was displayed, what action the user took, when, and in what session context) and constructs the evidence object as defined in Section 3. 5. The AS signs the evidence record and includes it in the issued access token. The following diagram illustrates this pattern: Client/Agent Authorization Server User | | | |-- authorization req --->| | | | | | |--- consent UI ---------->| | | (displayed_content) | | | | | |<-- user action ----------| | | (button_click, etc.) | | | | | | [capture evidence] | | | [sign with as_signature]| | | | |<-- access token --------| | | (with evidence) | | | | | Figure 5 6.1.2. Consent UI to Evidence Field Mapping Each field in the evidence object corresponds to a specific event during the consent interaction: Liu, et al. Expires 25 December 2026 [Page 13] Internet-Draft OAuth Authorization Evidence June 2026 +==============+===================+========================+ | Consent UI | Evidence Field | Description | | Event | | | +==============+===================+========================+ | AS renders | displayed_content | The text shown to the | | consent page | | user describing the | | | | requested operation | +--------------+-------------------+------------------------+ | User | user_action | How the user responded | | confirms or | | (button click, | | denies | | biometric, PIN, etc.) | +--------------+-------------------+------------------------+ | Confirmation | timestamp | Server-side time when | | timestamp | | the user's action was | | | | received | +--------------+-------------------+------------------------+ Table 5: Consent UI Event to Evidence Field Mapping 6.1.3. Example: JWT Grant Interaction Response Flow The JWT Grant Interaction Response ([I-D.parecki-oauth-jwt-grant-interaction-response]) defines a mechanism for AI agents to obtain user consent from an external Authorization Server. The following sequence shows how evidence is collected during this flow: 1. An AI agent sends a token request to the AS using a JWT authorization grant ([RFC7523]), including the requested scope and authorization_details. 2. The AS validates the agent's identity and determines that user interaction is required. It responds with an interaction_required error containing an interaction_uri (a URL hosted by the AS for the consent interface) and a polling interval. 3. The agent opens the interaction_uri in the user's browser. The AS presents a consent page showing the interpreted operation (e.g., "Add items under $50 to cart on your behalf"). 4. The user reviews the displayed content and clicks "Allow". The AS captures: * displayed_content: the operation description shown on the consent page; * user_action: button_click; Liu, et al. Expires 25 December 2026 [Page 14] Internet-Draft OAuth Authorization Evidence June 2026 * timestamp: the server time of the click. 5. The AS constructs the evidence object, computes the as_signature per Section 3, and stores the evidence record. 6. The agent polls the token endpoint. Upon detecting that the user has completed interaction, the AS issues an access token containing the signed evidence object. AI Agent External AS User | | | |-- token request ->| | | | | |<- interaction_ | | | required | | | (interaction_ | | | uri, interval) | | | | | |-- open interaction_uri in browser ------------>| | | | | |--- consent UI ------------>| | | "Add items under $50 | | | to cart on your behalf"| | | | | |<-- user clicks [Allow] ----| | | | | | [capture evidence fields] | | | [compute as_signature] | | | | |-- poll token --->| | | endpoint | | | | | |<- access token ---| | | (with evidence) | | | | | Figure 6 6.1.4. Applicability to Other Flows The consent-to-evidence pattern described above applies to any OAuth flow that involves user interaction. For example: * *Authorization Code Grant*: The AS presents a consent screen during the /authorize redirect. Evidence is collected when the user approves or denies the request. Liu, et al. Expires 25 December 2026 [Page 15] Internet-Draft OAuth Authorization Evidence June 2026 * *CIBA (Client-Initiated Backchannel Authentication)*: The AS delivers a consent request to the user's authentication device (e.g., push notification). Evidence captures the user's out-of- band confirmation action. * *Consent-Only Flow*: When the user already holds a valid session and the AS determines that only operation-specific consent is needed (not re-authentication), the AS presents a targeted consent prompt. Evidence records the scoped approval. Flows that do not involve user interaction (e.g., Client Credentials Grant without user context) cannot produce evidence records, since there is no user confirmation to record. Such flows MAY still use the audit_trail sub-object (Section 4) for semantic traceability without user confirmation evidence. 6.2. Evidence Generation When issuing an access token with evidence, the AS MUST: 1. Record the exact content displayed to the user during consent; 2. Capture the user's confirmation action and timestamp; 3. Generate a unique evidence identifier; 4. Sign the evidence fields (id and user_confirmation) with the AS's private key using JCS canonicalization; 5. Include the authorization_evidence authorization details in the access token. 7. Resource Server Processing 7.1. Evidence Verification Resource Servers MAY verify the evidence object by: 1. Extracting the as_signature from the evidence; 2. Verifying the signature using the AS's public key; 3. Confirming that the evidence id and timestamp are consistent with the token's iat claim (i.e., the user confirmation occurred before or at token issuance); Liu, et al. Expires 25 December 2026 [Page 16] Internet-Draft OAuth Authorization Evidence June 2026 Note: The displayed_content field records what was shown to the user during consent. The RS typically does not have direct knowledge of the consent interaction and therefore cannot independently verify this field. Instead, the RS relies on the AS signature as proof that the AS witnessed the user's consent to the described operation. 7.2. Audit Logging Resource Servers SHOULD log evidence information for audit purposes, including: * Evidence ID; * User confirmation timestamp; * Displayed content summary; * Operation performed; * Outcome (success/failure). 8. Security Considerations This section discusses security considerations specific to authorization evidence in OAuth 2.0. General OAuth 2.0 security considerations, including token threats and countermeasures, are described in [RFC6819]. 8.1. Signature Verification The AS signature over the evidence fields (id and user_confirmation) is critical for evidence integrity. Implementations MUST: * Use strong cryptographic algorithms (e.g., RS256, ES256); * Protect AS signing keys appropriately; * Rotate keys periodically with proper key management. 8.2. Evidence Tampering and Trust in the AS The evidence object is protected by the access token's signature. However, the as_signature field provides an additional layer of protection specifically for the user confirmation record. It is important to understand the trust boundary of the evidence mechanism: the as_signature provides cryptographic proof that the AS *recorded* a user confirmation. It does not independently prove that Liu, et al. Expires 25 December 2026 [Page 17] Internet-Draft OAuth Authorization Evidence June 2026 the user *actually* consented. The AS controls both the consent interaction and the signing key, so a compromised or malicious AS could fabricate evidence records. Trust in the evidence record therefore depends on trust in the AS and its operational security. Deployments requiring stronger non-repudiation guarantees SHOULD supplement this mechanism with user-side signatures or independent consent auditing. 8.3. Replay Attacks Evidence records are bound to specific access tokens. The evidence ID and timestamp help detect attempts to reuse evidence across different authorization contexts. 8.4. Token-Evidence Binding The evidence object is embedded in a signed access token ([RFC9068]), which provides integrity protection at the token level. The inner as_signature provides a second, independent integrity layer specifically over the user confirmation record. This dual-signature design ensures that: * Evidence cannot be moved from one token to another without detection (the token signature would not cover the new evidence); * Evidence fields cannot be modified within a valid token (the inner AS signature would be invalidated); * Evidence can be independently verified even when extracted from the token (e.g., via introspection) using the as_signature. Implementations MUST NOT copy an evidence object from one access token into another without re-validating the as_signature and confirming that the evidence id and timestamp are consistent with the new token's context. The dual-signature design described above applies to signed JWT access tokens ([RFC9068]). When opaque (reference) tokens are used, the evidence object is not embedded in the token itself and MUST be retrieved by the RS via token introspection ([RFC7662]) or a dedicated evidence retrieval endpoint. In this case, the as_signature provides the sole integrity protection for the evidence record, and implementations MUST ensure that the transport between the RS and the introspection or retrieval endpoint is protected with TLS. Liu, et al. Expires 25 December 2026 [Page 18] Internet-Draft OAuth Authorization Evidence June 2026 8.5. Cross-Domain Evidence Verification In cross-domain scenarios where the RS is in a different trust domain than the AS, the RS must be able to verify the as_signature using the AS's public key. Implementations SHOULD: * Publish the AS's evidence signing keys at a well-known JWKS endpoint ([RFC7517]) accessible to the RS; * Include a kid (Key ID) in the JWS header of the as_signature to enable key selection; * Support key caching at the RS with appropriate cache invalidation to balance performance and key freshness. When the AS and RS belong to different administrative domains, trust establishment for the evidence signing key MAY be facilitated through a trust framework, federation agreement, or explicit key distribution mechanism. 8.6. Privacy Considerations Evidence records contain information about user consent interactions, including what was displayed to the user and how they responded. Implementations should consider applicable data protection requirements when storing and processing evidence records. 9. IANA Considerations 9.1. OAuth Authorization Details Type Registration This specification registers the following authorization details type in the "OAuth Authorization Details Types" registry established by [RFC9396]: Type: authorization_evidence Description: Authorization evidence and audit trail information using the enriched response pattern, providing cryptographic proof of user consent for authorization proof and audit purposes. Change Controller: IETF Specification Document: Section 3 of this document 10. References 10.1. Normative References Liu, et al. Expires 25 December 2026 [Page 19] Internet-Draft OAuth Authorization Evidence June 2026 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012, . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015, . [RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013, . [RFC8785] Rundgren, A., Jordan, B., and S. Erdtman, "JSON Canonicalization Scheme (JCS)", RFC 8785, DOI 10.17487/RFC8785, June 2020, . [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, . [RFC9068] Bertocci, V., "JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens", RFC 9068, DOI 10.17487/RFC9068, October 2021, . [RFC9396] Lodderstedt, T., Richer, J., and B. Campbell, "OAuth 2.0 Rich Authorization Requests", RFC 9396, DOI 10.17487/RFC9396, May 2023, . 10.2. Informative References Liu, et al. Expires 25 December 2026 [Page 20] Internet-Draft OAuth Authorization Evidence June 2026 [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", RFC 7662, DOI 10.17487/RFC7662, October 2015, . [RFC7523] Jones, M., Campbell, B., and C. Mortimore, "JSON Web Token (JWT) Profile for OAuth 2.0 Client Authentication and Authorization Grants", RFC 7523, DOI 10.17487/RFC7523, May 2015, . [I-D.liu-oauth-rego-policy] Liu, D., "Rego Policy Language for OAuth 2.0", Work in Progress, Internet-Draft, draft-liu-oauth-rego-policy-00, June 2026, . [I-D.parecki-oauth-jwt-grant-interaction-response] Parecki, A., Campbell, B., and D. Liu, "JWT Authorization Grant with Interaction Response", Work in Progress, Internet-Draft, draft-parecki-oauth-jwt-grant-interaction- response-00, June 2026, . [I-D.ietf-oauth-identity-assertion-authz-grant] Ying, K. and B. Campbell, "OAuth 2.0 Identity Assertion Authorization Grant", Work in Progress, Internet-Draft, draft-ietf-oauth-identity-assertion-authz-grant, January 2026, . Appendix A. Complete Example The following shows a complete access token with authorization_details containing both authorization_evidence and rego_policy authorization details types: This example illustrates how the authorization_evidence type complements the rego_policy type ([I-D.liu-oauth-rego-policy]). While the Rego policy defines *what operations are permitted* (the behavioral constraint contract), the authorization evidence records *why those operations were authorized* (the user's explicit consent). Together, they enable a Resource Server to enforce fine-grained policy while maintaining a verifiable audit trail linking each authorized action back to user intent. The act.sub value uses the wit:// URI scheme to identify the acting agent by its workload identity, as defined in the Identity Assertion Authorization Grant Liu, et al. Expires 25 December 2026 [Page 21] Internet-Draft OAuth Authorization Evidence June 2026 ([I-D.ietf-oauth-identity-assertion-authz-grant]). The hash suffix provides a collision-resistant binding between the URI and the agent's attestation evidence. { "iss": "https://as.example.com", "sub": "user_12345", "aud": "https://api.shop.example", "exp": 1731369540, "iat": 1731320700, "jti": "urn:uuid:token-abc-123", "act": { "sub": "wit://myassistant.example/sha256.abc123..." }, "authorization_details": [ { "type": "authorization_evidence", "evidence": { "id": "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6", "user_confirmation": { "displayed_content": "Add items under $50 to cart", "user_action": "confirmed_via_button_click", "timestamp": 1731320595 }, "as_signature": "eyJhbGciOiJFUzI1NiJ9..MEUCIQDx...", "audit_trail": { "semantic_expansion_level": "medium", "proposal_ref": "urn:uuid:proposal-xyz" } } }, { "type": "rego_policy", "policy": { "type": "rego", "uri": "https://as.example.com/policies/policy-cart-50", "entry_point": "allow" } } ] } Figure 7 Liu, et al. Expires 25 December 2026 [Page 22] Internet-Draft OAuth Authorization Evidence June 2026 Acknowledgments The authors would like to thank Brian Campbell for his valuable feedback and insightful discussions during the development of this specification. His contributions helped shape key design decisions. Authors' Addresses Dapeng Liu Alibaba Group Email: max.ldp@alibaba-inc.com Hongru Zhu Alibaba Group Email: hongru.zhr@alibaba-inc.com Suresh Krishnan Cisco Email: suresh.krishnan@gmail.com Aaron Parecki Okta Email: aaron@parecki.com Liu, et al. Expires 25 December 2026 [Page 23]