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asharaut@amazon.com

next generation unicorn sparkling distributed ledger This document specifies an extension to the OAUTH-TXN-TOKENS to support agent context propagation within Transaction Tokens for agent-based workloads. The extension defines the use of the act field to identify the agent performing the action, and leverages the existing sub field (as defined in the base Transaction Tokens specification) to represent the principal. The sub field is populated according to the rules specified in OAUTH-TXN-TOKENS, based on the 'subject_token' provided in the token request. For autonomous agents operating independently, the sub field represents the agent itself. These mechanisms enable services within the call graph to make more granular access control decisions, thereby enhancing security. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Source for this draft and an issue tracker can be found at .

Introduction Traditional zero trust authorization systems face new challenges when applied to AI agent workloads. Unlike conventional web services, AI agents possess capabilities for autonomous operation, behavioral adaptation, and dynamic integration with various data sources. These characteristics may lead to decisions that extend beyond their initial operational boundaries. Existing zero trust models, which effectively manage permissions and access scopes for traditional web services, require enhancement to address the unique properties of AI agents. Authorization systems must evaluate each AI agent interaction independently, considering both the immediate context and intended action. This necessitates more sophisticated approaches to policy enforcement, behavioral monitoring, and audit tracking to maintain security governance. Transaction Tokens (Txn-Tokens) are short-lived, signed JSON Web Tokens RFC7519 that convey identity and authorization context. However, the current Txn-Token format lacks sufficient context for services within the call chain to implement fine-grained access control policies for agent-based workflows. Specifically, it does not provide adequate information about the AI agent's identity or its initiating entity, limiting transaction traceability. With this extension, Transaction Tokens will carry agent identity information which will help in better traceability for AI Agent's actions deep down the web service graph connecting multiple web services involved in completing a transaction in distributed systems. This document defines three new contexts within the Transaction Token to address these limitations:

1. The act claim, which identifies the AI agent performing the action, aligning with OAuth 2.0 Token Exchange RFC8693 terminology for actor tokens
2. The sub claim, as defined in OAUTH-TXN-TOKENS, which represents the principal on whose behalf the transaction is being performed. The population of this field follows the rules specified in the base Transaction Tokens specification, based on the 'subject_token' provided in the token request.
3. An optional agentic_ctx claim. The value of this claim, if present, MUST be a JSON object. The agentic_ctx claim conveys attributes about the agent and its operational constraints that are relevant to authorization, auditing, and policy evaluation.

This extension leverages the existing Txn-Token infrastructure to enable secure propagation of AI agent context throughout the service graph.

Conventions and Terminology 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.

Terminology Agentic-AI: AI Agentic applications are software applications that utilize Large Language Models (LLM)s and plans, reasons,and takes actions independently to achieve complex, multi-step goals with minimal human oversight. Workload: An independent computational unit that can autonomously receive and process invocations, and can generate invocations of other workloads. Examples of workloads include containerized microservices, monolithic services and infrastructure services such as managed databases. Trust Domain: A collection of systems, applications, or workloads that share a common security policy. In practice this may include a virtually or physically separated network, which contains two or more workloads. The workloads within a Trust Domain may be invoked only through published interfaces. Call Chain: A sequence of synchronous invocations that results from the invocation of an external endpoint. External Endpoint: A published interface to a Trust Domain that results in the invocation of a workload within the Trust Domain. This is the first service in the call chain where request starts. Transaction Token (Txn-Token): A signed JWT with a short lifetime, providing immutable information about the user or workload, certain parameters of the call, and specific contextual attributes of the call. The Txn-Token is used to authorize subsequent calls in the call chain. Transaction Token Service (Txn-Token Service): A special service within the Trust Domain that issues Txn-Tokens to requesting workloads. Each Trust Domain using Txn-Tokens MUST have exactly one logical Txn-Token Service.

Protocol overview

Transaction Flow This section describes the process by which an agent application obtains a Transaction Token, either acting autonomously or on behalf of a principal. The external endpoint requests a Txn-Token following the procedures defined in OAUTH-TXN-TOKENS, augmented with additional context for agent identity and, when applicable, principal identity.

Agent Application Transaction Flows The Transaction Token creation process varies depending on the presence of a principal.

Principal-Initiated Flow When a principal initiates the workflow, the following steps occur:

1. The principal invokes the agent application to perform a task.
2. The agent application calls an external endpoint. External endpoint throws back OAuth challenges.
3. The agent application authenticates using an OAuth 2.0 Auth code flow RFC6749 access token. The access token contains subject and clientId claims as per RFC9068.
4. The external endpoint submits the received access token along with its Subject token to the Txn-Token Service. Subject token requirements are specified in OAUTH-TXN-TOKENS.
5. The Txn-Token Service validates the access token.
6. The Txn-Token Service populates the Txn-Token's sub claim following the rules specified in OAUTH-TXN-TOKENS. The sub claim is determined based on the subject_token provided in the request, according to the conditions and rules defined in the base Transaction Tokens specification. This ensures that the principal is properly represented in the Txn-Token.
7. The Txn-Token Service copies the access token's clientId claim to the Txn-Token's act field. Any nested structure within the clientId claim is preserved. If the access token contains an act claim, that value MAY be used instead of clientId.
8. The Txn-Token Service issues the Txn-Token to the requesting workload.

Autonomous Flow When the agent application operates autonomously, the following steps occur:

1. The agent application initiates a task based on an event or scheduled assignment.
2. The agent application calls an external endpoint. OAuth challenge flow starts.
3. The agent application authenticates using an OAuth 2.0 RFC6749. When an autonomous agent (no human resource owner) needs to call another resource server using OAuth, it follows the Client Credentials Grant defined explicitly in RFC6749.
4. The agent application uses the access token to call the external endpoint.
5. The external endpoint submits the received access token along with its Subject token to the Txn-Token Service. Subject token requirements are specified in OAUTH-TXN-TOKENS.
6. The Txn-Token Service validates the access token.
7. The Txn-Token Service populates the Txn-Token's sub claim following the rules specified in OAUTH-TXN-TOKENS. The sub claim is determined based on the subject_token provided in the request. For autonomous agents, this typically represents the agent's own identity.
8. The Txn-Token Service copies the access token's sub or clientId claim to the Txn-Token's act field. Any nested structure is preserved. The act field identifies the agent performing the autonomous action.

Flow Diagrams

Principal-Initiated Flow Based on the updated flow, here's a more detailed RFC-style flow diagram: | | | | | | | | | | | Call external API | | | |---------->| | | | | | | | | | OAuth Challenge | | | |<----------| | | | | | | | | | Initiate Auth Code Flow | | | |------------------------->| | | | | | | | | Auth Code | | | |<-------------------------| | | | | | | | | Exchange code for token | | | |------------------------->| | | | | | | | | Access Token (AT1) | | | | w/ sub, clientId claims | | | |<-------------------------| | | | | | | | | Call with AT1 | | | |---------->| | | | | | | | | | | Request Txn-Token | | | | with AT1, Subject token | | | | as param | | | | |--------------------------->| | | | | | | | | | Validate AT1 | | | | Extract claims | | | | Set sub from Subject token | | | | Set act from AT1.clientId | | | | | | | | | | | | | | | | | | | | | | | Txn-Token | | | | |<---------------------------| | | | | | Legend: ----> : Request flow <---- : Response flow | : Component boundary ]]> Notes: 1. AT1 refers to the access token obtained by Agent App 2. The External Endpoint uses its own access token to call Txn-Token Service 3. AT1 is passed as a parameter in the Txn-Token request 4. The flow shows detailed OAuth 2.0 Authorization Code flow steps 5. Token validation and claim extraction steps are shown in the Txn-Token Service

Autonomous Flow | | | | | | | | OAuth Challenge | | |<----------| | | | | | | | Client Credentials Grant | | |------------------------->| | | | | | | Access Token (AT1) | | | sub, aud claims | | |<-------------------------| | | | | | | Call with AT1 | | |---------->| | | | | | | | | Request Txn-Token | | | with AT1, Subject token | | | as param | | | |--------------------------->| | | | | | | | Validate AT1 | | | Extract claims | | | Set sub from aud | | | Set act.sub from clientId or sub | | | | | | | | | | | | | | Txn-Token | | | |<---------------------------| | | | | Legend: ----> : Request flow <---- : Response flow | : Component boundary + : Internal process --+ : Self-triggered event Notes: * AT1: Access token obtained via Client Credentials Grant * External Endpoint uses subject token for authenticating itself to Txn-Token Service * AT1 is included as parameter in Txn-Token request * Self-triggered events can be scheduled tasks or external triggers * Token validation includes signature and claims verification ]]>

Replacement tokens Txn-Token Service provides capability to get a replacement Txn-Token as defined in the OAUTH-TXN-TOKENS.replacement flow. If the original Txn-Token used to get replacement token contains 'actor' and 'principal' claims then in the replaced Txn-Token, the values of the 'actor' and 'principal' MUST remain unchanged similar to 'txn', sub and 'aud' claims.

Txn-Token Format

JWT Header No changes to the JWT header from the base specification: typ MUST be txntoken+jwt, with a signing key identifier such as kid.

JWT Body Claims The Txn-Token body augments the base claim set with the act field for agent context. Existing claims like txn, sub, aud, iss, iat, exp, scope, tctx, and req_wl retain identical semantics, population rules, and immutability guarantees as defined in OAUTH-TXN-TOKENS. In this example, the agent is 3rd party and not part of trust domain. It hits API Gateway in trust domain and API Gateway requests Txn-Token from Txn-token Service using access token received from 3P agent and its own subject token (to authenticate with Txn-Token Service). Requesting workload is API Gateway. Agent is agent-identity-1 (clientId in the access token issued to 3P agent to act on behalf of user:alice)

Agentic Context The Txn-Token MAY contain an agentic_ctx claim. Txn-Tokens are increasingly used in environments where transactions are executed by or with the assistance of autonomous or semi-autonomous agents (for example, Large Language Model (LLM)–based agents, workflow orchestrators, and policy-driven automation components). In such deployments, relying exclusively on subject identity and generic transaction parameters is insufficient to make robust authorization decisions. Additional information about the agent that is interpreting and acting on the transaction is often required.

Integration with OAuth Rich Authorization Requests When the Authorization Server (AS) supports Rich Authorization Requests (RAR) as defined in [RFC9396], the authorization details captured during the initial consent flow provide high-fidelity context for downstream agentic enforcement. The RAR mechanism allows a Resource Owner to grant permissions for specific, fine-grained actions (e.g., "Allow Agent to search only 'Research' folder") which are then encoded in the Access Token.

Processing RAR Context The Txn-Token Service (TTS) SHOULD extract relevant authorization details from the authorization_details claim of the subject_token and encapsulate them within the agentic_ctx. This ensures that the agent's execution environment remains bound by the specific constraints approved by the user.

Data Mapping and Enrichment

1. Extraction: The TTS extracts the RAR array from the incoming Access Token.
2. Encapsulation: The TTS SHOULD include these details in the agentic_ctx under a standardized key to allow downstream services to distinguish between general agent metadata and explicit user-granted permissions.
3. Policy Deferral: This pattern allows the AS to capture intent without necessarily needing the domain-specific logic to enforce it; enforcement is deferred to the microservices deep in the call chain that receive the Txn-Token.

Benefits of RAR Integration

• Consent Propagation: User-consented details are cryptographically bound to the Txn-Token, ensuring consent is honored throughout the service graph.
• Granular Control: Services can make informed decisions based on the specific "type" and "actions" authorized in the original RAR object.
• Reduced Complexity: Centralizing complex consent capture at the AS while distributing enforcement via the agentic_ctx reduces the architectural burden on individual workloads.

Example of agentic_ctx with additional context

Multi-agent flows In complex agentic workflows, a primary agent (the "Delegator") may delegate sub-tasks to one or more secondary agents ("Delegatees"). This document defines a mechanism to preserve the delegation lineage across these transitions. Note that preserving lineage is optional.

Agent-to-Agent Delegation When an agent (the "Delegator") invokes another agent (the "Delegatee") to perform a sub-task, it SHOULD NOT pass its own Transaction Token to the Delegatee. Instead, the Delegator MUST obtain a narrowed Transaction Token for the Delegatee using the replacement flow defined in OAUTH-TXN-TOKENS. The Delegator SHOULD request a restricted scope or purp (Purpose) that is specific to the sub-task assigned to the Delegatee.

The 'actchain' (Actor Chain) Claim The actchain claim is an OPTIONAL top-level JSON Web Token (JWT) claim that provides a cryptographic trace of the delegation path. It is represented as an ordered array of JSON objects, where each object represents a previous agent in the call chain.

Claim structure Each object within the actchain array MUST contain the following members: * sub (Subject): REQUIRED. The identity of the delegating agent. * iat (Issued At): OPTIONAL. A timestamp indicating when the delegating agent initiated its portion of the transaction. * iss (Issuer): OPTIONAL. The issuer of the token that identified the delegating agent. This might be required in case of multiple Txn Token Services being present across domains and token is passed across domains.

Delegation via Replacement Flow When an agent requests a narrowed Transaction Token for a sub-agent, the Transaction Token Service (TTS) MUST follow the replacement flow procedures defined in OAUTH-TXN-TOKENS with the following modifications:

• Subject Immutability: The txn and sub (principal) claims MUST be copied from the subject_token to the new Transaction Token without modification.
• Chain Progression: The TTS MUST extract the act claim from the incoming subject_token. This extracted object MUST be appended to the end of the actchain array in the new token. If no actchain existed in the subject_token, a new array is created containing only the extracted act object.
• New Actor Assignment: The top-level act claim of the new token MUST be set to the identity of the Delegatee (the sub-agent).

Multi-agent example JWT body claims This example represents a delegated state: a human principal initiated a task via a Researcher Agent, which then delegated a specific action to a Search Agent.

Security Considerations

1. All the security considerations mentioned in OAUTH-TXN-TOKENS apply.
2. Token Replay Protection Implementations MUST enforce strict token lifetime validation. The short-lived nature of Transaction Tokens helps mitigate replay attacks, but implementations SHOULD also consider:
   • Implementing token tracking mechanisms within trust domains
   • Validating token usage context
3. Actor Identity Security
   • Implementations MUST validate act claims in tokens
   • The Txn-Token Service MUST verify the authenticity of actor context before token issuance
   • During replacement flow, Txn-Token Service MUST NOT modify the act field in the incoming Txn-Token
4. Principal Context Protection
   • Systems MUST prevent unauthorized modifications to the sub claim during token propagation. Txn-Tokens are cryptographically signed to ensure integrity.
   • During replacement flow, Txn-Token Service MUST NOT modify the sub claim in the incoming Txn-Token
   • The Txn-Token Service MUST follow the subject population rules defined in OAUTH-TXN-TOKENS to ensure proper principal representation
5. Transaction Chain Integrity
   • Implementations MUST maintain cryptographic integrity of the token chain
   • Services MUST validate tokens at trust domain boundaries
   • Systems MUST implement protection against token tampering during service-to-service communication
6. AI Agent Specific Controls
   • Implementations MUST enforce scope boundaries for AI agent operations
   • Systems SHOULD implement behavioral monitoring for AI agent activities by logging act and sub claims in audit logs
   • Systems MUST maintain audit trails of AI agent activities
7. Token Transformation Security
   • The Txn-Token Service MUST validate all claims during access token to Txn-Token conversion
   • Implementations MUST verify signatures and formats of all tokens
   • Systems MUST prevent unauthorized manipulation during token transformation
   • The Txn-Token Service MUST ensure that the act field accurately represents the agent identity from the access token
8. Replacement Token Considerations
   • Systems MUST verify the authenticity and validity of original tokens before replacement
   • Systems MUST implement controls to prevent unauthorized replacement requests
   • The immutability of act and sub claims during replacement ensures consistent identity context throughout the transaction lifecycle
9. Infrastructure Security
   • All component communications MUST use secure channels
   • Implementations MUST enforce strong authentication of the Authorization Server
   • Systems MUST implement regular rotation of cryptographic keys
   • Trust domain boundaries MUST be clearly defined and enforced
10. Multi-Agent Considerations:
    • Chain Depth and Bloat: Deeply nested agent calls can lead to significant JWT size increases, potentially impacting HTTP header limits. The TTS MAY impose a maximum depth for the actchain. If the maximum depth is exceeded, the TTS MUST either reject the request or truncate the oldest entries in the chain, provided that a "truncated" flag is added to the claim to alert downstream services of the loss of provenance.
    • Privilege Escalation: A Delegator MUST NOT be able to request a replacement token with broader permissions or a higher-tier principal than what is asserted in its own subject_token. The TTS MUST validate that the requested scope and purp are a logical subset of the original token.
    • The TTS MUST verify that the workload requesting a replacement token is the entity identified in the act claim of the subject_token. This prevents an unauthorized workload from "injecting" itself into a transaction chain or extending a chain it is not part of.
    • During the replacement flow, the TTS MUST NOT allow the modification of the sub (principal) or txn claims. These fields provide the "anchor" for the entire transaction; any modification would effectively initiate a new transaction, requiring a fresh authentication event rather than a replacement flow.

References

Normative References RFC2119 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, https://www.rfc-editor.org/rfc/rfc2119. RFC8174 Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, https://www.rfc-editor.org/rfc/rfc8174 RFC6749 Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012, https://www.rfc-editor.org/rfc/rfc6749. RFC7519 Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, https://www.rfc-editor.org/rfc/rfc7519. RFC7515 Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, https://www.rfc-editor.org/rfc/rfc7515. RFC8693 Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J., and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693, DOI 10.17487/RFC8693, January 2020, https://www.rfc-editor.org/rfc/rfc8693. RFC9068 Bertocci, V., "JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens", RFC 9068, DOI 10.17487/RFC9068, October 2021, https://www.rfc-editor.org/rfc/rfc9068. RFC9396 T. Lodderstedt, J. Richer, B. Campbell, "OAuth 2.0 Rich Authorization Requests", RFC 9396, DOI 10.17487/RFC9396, May 2023, https://www.rfc-editor.org/rfc/rfc9396. OAUTH-TXN-TOKENS Atul Tulshibagwale, George Fletcher, Pieter Kasselman, "OAuth Transaction Tokens", https://drafts.oauth.net/oauth-transaction-tokens/draft-ietf-oauth-transaction-tokens.html

Acknowledgments The authors would like to thank the contributors and the OAuth working group members who gave valuable input to this draft.

Contributors name: Atul Tulshibagwale org: SGNL email: atul@sgnl.ai