feat: validate CTE actor token pairing and surface act claim for delegation/impersonation#122
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kishore7snehil
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The act-claim enrichment in custom_token_exchange ran _verify_and_decode_jwt with no error handling, so a present-but-undecodable id_token turned an already-issued exchange into a generic TOKEN_EXCHANGE_FAILED. It also skipped the normalized issuer check the login path applies before trusting claims. Wrap the enrichment so any decode/verify failure leaves act=None instead of failing the exchange, and apply the issuer check before reading the claim. Rewrite the opaque-token test (it never exercised the decode path) and add coverage for the undecodable-id_token and issuer-mismatch cases.
nandan-bhat
reviewed
Jun 23, 2026
…urcing Add local empty/whitespace guards for subject_token_type and actor_token so they fail with a clear INVALID_TOKEN_FORMAT instead of a generic round-trip error from the token endpoint, matching the existing subject_token check. Add tests for both cases. Document that response.act is read from the id_token and that Auth0 writes the same act onto the access token (verified against the platform token dialects), noting the access token may be opaque. Add a comment on the login path noting act reaches the session user via UserClaims. Rename the refresh test to reflect that it pins the state-merge behavior the refresh path uses.
rmad17
reviewed
Jun 24, 2026
rmad17
reviewed
Jun 24, 2026
rmad17
approved these changes
Jun 25, 2026
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📋 Changes
This PR completes Custom Token Exchange (CTE) Delegation/Impersonation support (RFC 8693) in auth0-server-python. CTE input validation moves into the exchange methods so callers get typed
CustomTokenExchangeErrors with specific codes, theactor_token/actor_token_typepairing is enforced in both directions, and theactclaim from a delegation/impersonation exchange is surfaced to the developer.✨ Features
custom_token_exchangeandlogin_with_custom_token_exchangenow rejectactor_tokenwithoutactor_token_type(MISSING_ACTOR_TOKEN_TYPE) andactor_token_typewithoutactor_token(MISSING_ACTOR_TOKEN), matching how Auth0 enforces the pair.actclaim surfacing: When an exchange includes an actor token, the SDK verifies the returned ID token and exposes the RFC 8693 §4.1actclaim onTokenExchangeResponse.act(stateless) and on the persisted session user, readable back viaget_user()(session-creating).Bearer-prefixed tokens now raiseCustomTokenExchangeError(INVALID_TOKEN_FORMAT).🔧 API Changes
CustomTokenExchangeErrorCode.MISSING_ACTOR_TOKENTokenExchangeResponse.act: Optional[dict[str, Any]]custom_token_exchange/login_with_custom_token_exchangeand raisesCustomTokenExchangeErrorwith a specific code (INVALID_TOKEN_FORMAT,MISSING_ACTOR_TOKEN_TYPE,MISSING_ACTOR_TOKEN)📖 Documentation
examples/CustomTokenExchange.mdwithactread-back (stateless and session), the refresh-token suppression note, and theMISSING_ACTOR_TOKENerror code🧪 Testing
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