Authorization Server: DPoP Support (SEP-1932)#396
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…odelcontextprotocol#368) Client-anchored packaging: carries the shared DPoP foundation (dpopProof / dpopToken helpers, the createAuthServer DPoP core, and sep-1932.yaml) together with the client scenario, so it can merge first; the server (modelcontextprotocol#369) and authorization-server (modelcontextprotocol#370) scenarios are follow-ups that depend on it. DPoP is treated as a draft/not-yet-official feature (mirroring the WIF SEP-1933 scenario): the scenario's source is `introducedIn: DRAFT_PROTOCOL_VERSION` and it is registered in draftScenariosList (informational, not scored). It is NOT registered in EXTENSION_IDS, since the ext-auth DPoP extension is still on a branch rather than merged. Client checks (the two extension MUSTs, RFC 9449 §7.1 / §4.2-4.3): - sep-1932-client-dpop-auth-scheme — token presented with the DPoP scheme. - sep-1932-client-fresh-proof — a fresh, well-formed DPoP proof per request. The test MCP server judges the client via an opt-in DPoP middleware (dpopResourceAuth) passed through createServer's authMiddleware hook; a compliant example client (covered by the Client Draft Scenarios loop) plus deliberately- broken bearer/replay variants drive the pass/fail acceptance tests. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Server-provided nonces are optional in RFC 9449 (AS §8 "MAY", RS §9 "can also choose"), and the nonce-less flow is the common case. The single auth/dpop scenario hard-wired nonce enforcement on both the test AS and MCP server, so a plain nonce-less proof was never accepted end-to-end and a client that only does plain proofs was never exercised on its happy path. Parameterize DPoPClientScenario with `requireNonce` and register it twice: - auth/dpop (requireNonce=false) — nonce-less baseline; emits the three baseline checks (token-request-proof, dpop-auth-scheme, fresh-proof). - auth/dpop-nonce (requireNonce=true) — prior behavior; adds as-nonce and rs-nonce (five checks). Check IDs are reused (no new IDs, no sep-1932.yaml change); the two nonce checks are emitted only by auth/dpop-nonce, so traceability stays intact. Add auth-test-dpop-no-nonce.ts (nonce-incapable but otherwise compliant) asserting SUCCESS against auth/dpop — proof that a client with no nonce handling still completes DPoP when the server does not require a nonce. Baseline negatives stay on auth/dpop (nonce-independent); the two nonce negatives are re-pointed to auth/dpop-nonce. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Address review findings on the auth/dpop-nonce posture: - Record the token-request proof observation BEFORE the §8 nonce challenge, so a client that is challenged but does not retry is no longer mis-reported by token-request-proof as "never completed a token request" (its proof was just validated). (#2) - Record the resource-request jti/replay on ANY valid proof (before the §9 nonce gate), so fresh-proof is never asserted on zero evidence and a client that never honours the RS nonce fails ONLY rs-nonce. (modelcontextprotocol#5) - Require challengeIssued && honored for as-nonce/rs-nonce SUCCESS, closing a vacuous-pass path (a client that pre-sends the nonce is never challenged). (#3a) - Gate the AS nonce observation on the authorization_code exchange, matching recordTokenRequestProof (a refresh exchange must not satisfy §8). (#3c) - Collapse duplicate shared token-flow check IDs (token-request, pkce-*) that the §8 round-trip re-POST would otherwise emit twice. (modelcontextprotocol#4) - Example client: retry the token request only on a use_dpop_nonce error code, not any 400 carrying a DPoP-Nonce header (consistent with the RS path). (modelcontextprotocol#6) - Fix the DpopTokenRequestObservation docstring ("last write wins" → sticky-failure). (modelcontextprotocol#7) Adds an expectedSuccessSlugs option to the client test helper and tightens the two nonce negative tests to pin the now-clean behavior (token-request-proof SUCCESS for no-as-nonce; only rs-nonce fails for no-rs-nonce). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
- dedupeSharedChecks was masking failures: it kept the last occurrence of a duplicate check ID regardless of status and ran in BOTH postures, so a FAILURE on a challenged POST (or an earlier attempt in a restarted flow) was silently dropped. Replace with an exported, unit-tested collapseDuplicateChecks that prefers the MOST-SEVERE occurrence, and only apply it in the nonce posture (the baseline keeps genuinely distinct repeated attempts). (R5 #1) - Reword the token-request-proof description: it can be SUCCESS for a client that presented a valid proof but never obtained a token (challenged, no retry), so it no longer claims "obtaining a DPoP-bound access token". (R5 #2) - Reword the as-nonce/rs-nonce failure messages to cover a client that DID retry but whose retry proof was rejected (not only "did not retry"). (R5 #3) - Document the deliberate replay decision: recording jti on challenged requests means re-sending the identical proof across the challenge/retry boundary trips replay detection — a genuine RFC 9449 §4.2 jti-uniqueness violation. (R5 modelcontextprotocol#5) Adds src/scenarios/client/auth/dpop.test.ts unit-testing collapseDuplicateChecks (prefers failures, keeps INFO, preserves order) — the dedupe fix is now pinned. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
- Add an integration assertion that the §8/§9 double-POST is collapsed to one token-request/pkce-* entry each in auth/dpop-nonce, so the requireNonce gating of collapseDuplicateChecks can't be silently deleted or inverted (previously mutation-survivable). runClientAgainstScenario now returns the emitted checks so callers can make occurrence-level assertions (backward-compatible). - Docstring: note the severity ladder ranks SKIPPED below SUCCESS, and that equal-severity ties keep the last occurrence. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
…l#370) Follow-up on the DPoP client PR (shared foundation: createAuthServer DPoP core + dpopProof/dpopToken helpers). Adds an authorization-server scenario testing DPoP (SEP-1932 / RFC 9449): metadata (dpop_signing_alg_values_supported present, asymmetric-only), token binding (cnf.jkt + token_type=DPoP), and no-proof enforcement when dpop_bound_access_tokens is advertised. Probes a live AS via authorization_code + PKCE (auto-follows a direct redirect, falls back to an interactive callback) and returns four sep-1932-as-* checks (compliant run + four one-defect-isolation misbehaving configs). - authorization-server/dpop.ts (+ acceptance test, spec-references). - dpopToken: adds readTokenBinding() (reads token_type + cnf.jkt back out of a token response) — introduced here because this scenario is its only consumer. Depends only on the shared DPoP foundation; independent of the server PR. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
negotiateProofAlg fell back to ES256 for a present-but-non-array dpop_signing_alg_values_supported (e.g. the string "RS256"), contradicting its docstring and risking a token-binding mis-score for that malformed shape. Treat a present-but-non-array value as null (SKIP), like a non-empty list with no supported alg; only an absent/empty list still falls back to ES256. Defensive against malformed metadata; not independently exercised by a fixture (would need a malformed-metadata AS option), consistent with the htu-strip defensive fixes. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The round-4 non-array guard carved out `null` (advertised !== null), so metadata with "dpop_signing_alg_values_supported": null passed the support gate (which only tests === undefined), skipped the guard, and fell through to the ES256 fallback — the exact binding mis-score the fix targeted. Extract the negotiation to an exported pure function negotiateProofAlg(advertised) and treat ANY present-but-non-array shape (string, null, number, object) as malformed → null (SKIP). Only an empty array still falls back to ES256. Correct the docstring (an absent field never reaches here — the support gate SKIPs upstream). Add unit tests for every shape (array / empty / no-overlap / string / null / number / object), pinning the fix against a silent refactor regression. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Broaden the negotiateProofAlg fallback test to also assert undefined → ES256
and correct its title ("empty array or absent field") — the contract covers
both, though absent is gated upstream in the scenario.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This was referenced Jul 7, 2026
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Overview
Conformance tests for DPoP support (SEP-1932 / RFC 9449) on the authorization server side.
Builds on the shared DPoP test helpers introduced in the client PR (#394). Review that one first — this PR sits on top of it.
Closes #370.
What it tests
That an authorization server correctly advertises and implements DPoP. The scenario drives a real authorization-code + PKCE flow and checks the server:
dpop_signing_alg_values_supportedin its metadata (RFC 9449 §5.1).none, no symmetric algorithms.cnf.jktmatches the presented proof,token_type: DPoP).The scenario is support-gated: an authorization server that doesn't advertise DPoP is not a DPoP server, so it's skipped rather than failed.
Each check is proven to pass (compliant example authorization server) and to fail (misbehaving configurations), with an automated acceptance suite.
Scope
Authorization-server behaviour only — metadata and token issuance. Proof validation at the resource is covered by the MCP-server PR (#369); client presentation by the client PR (#394).
Notes