feat(validator): parse and expose On-Behalf-Of Token Exchange claims (RFC 8693) - #407
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…(RFC 8693) Add first-class validation support for tokens issued via On-Behalf-Of / Token Exchange (RFC 8693). RegisteredClaims now includes the act (actor) chain, azp, org_id, and org_name, populated automatically during validation. Add ValidatedClaims helpers CurrentActor(), DelegationChain(), and HasActor() that distinguish the current actor (for authorization, per RFC 8693 §4.1) from the informational delegation chain (for audit). Reject delegation chains deeper than 5 levels as malformed.
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+ Coverage 94.42% 94.51% +0.08%
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The cnf claim is now extracted in extractSupplementaryClaims alongside act, azp, and the organization claims, so the standalone extractConfirmationClaim method is unused and flagged by the linter. Remove it and fold its cnf test coverage into the extractSupplementaryClaims tests.
kishore7snehil
requested changes
Jul 22, 2026
- Decode cnf and act independently so a malformed act can no longer drop the cnf claim and silently downgrade a DPoP-bound token - Add WithMaxActorChainDepth option (positive-only, default 5) so the delegation chain depth limit is configurable instead of a fixed const - Stop DelegationChain at the first empty subject so it agrees with HasActor and CurrentActor on what an empty subject means - Align docs and comments with the invalid_claims error actually returned - Add end-to-end ValidateToken tests for actor/org/azp, over-depth rejection, configured depth, and cnf survival with a malformed act
kishore7snehil
requested changes
Jul 23, 2026
…n error Per RFC 8693 §4.1 generic verification must not fail on the act claim, so an actor with an empty sub no longer needs handling at ValidateToken. Change DelegationChain to return ([]string, error): it walks the full chain and returns ErrMalformedDelegationChain along with the subjects collected so far when an actor has an empty sub, instead of silently truncating. HasActor and CurrentActor keep their existing empty-sub semantics.
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📝 Checklist
🔧 Changes
Adds first-class validation support for access tokens issued through On-Behalf-Of / Token Exchange (RFC 8693), for example when an MCP server exchanges an incoming user token for one scoped to a downstream API. This SDK validates and inspects such tokens; performing the exchange itself is done by the authorization server, not this middleware.
These claims are now parsed automatically during validation, so no extra configuration is required.
validator.RegisteredClaims(new fields, additive)Act *Actor— theact(actor) claim chain per RFC 8693 §4.1AuthorizedParty string— theazpclaimOrgID string— theorg_idclaimOrgName string— theorg_nameclaimNew
validator.ActortypeModels the nested
actclaim:Subject(sub), optionalIssuer(iss), and a nestedAct *Actorfor the prior actor.New helpers on
validator.ValidatedClaimsCurrentActor() string— the current actor (outermostact.sub), the client that performed the most recent exchange. Per RFC 8693 §4.1, this is the only actor value that may be used for access-control decisions.DelegationChain() []string— the full actor chain ordered from current to original, intended for audit and logging only.HasActor() boolThe API is shaped so the safe call (
CurrentActor) is the obvious one, andDelegationChainis explicitly documented as audit-only, matching the RFC 8693 §4.1 guidance that nested actors must not drive authorization.Delegation chains are limited to 5 levels; a token whose
actclaim nests more than 5 actors is rejected as aninvalid_claimsvalidation error.All changes are additive. No existing fields, signatures, or behavior changed, and no new dependencies or network calls are introduced. Extraction of
act,azp,org_id, andorg_nameis folded into the existing single payload decode alongside thecnfclaim.📚 References
actclaim)🔬 Testing
CurrentActor,DelegationChain, andHasActorhelpers cover the no-actor, empty-subject, single-exchange, and chained-exchange cases (validator/claims_test.go).invalid_claims), and a malformed token (validator/validator_test.go).go test ./...(865 tests),go vet ./...clean,gofmtclean.