Server Auth: DPoP Proof Validation (SEP-1932)#395
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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>
…ocol#369) Follow-up on the DPoP client PR (shared foundation). Adds the server-role conformance for SEP-1932 / RFC 9449: the framework acts as a DPoP client against the MCP server under test and emits the sep-1932-server-* checks across the RFC 9449 §4.3 validation surface — proof validation, the ±5-minute iat window, asymmetric-only algorithms, the 401 + WWW-Authenticate challenge, token audience validation under DPoP, and the optional server-provided nonce. - src/scenarios/server/auth/dpop.ts (+ test, spec-references): the scenario. - examples/servers/typescript/sep-1932-{compliant,broken}-server.ts: passing and failing fixtures proving every check passes and fails. - Registered in the pending + all-client scenario lists. Depends only on the shared DPoP foundation (dpopProof/dpopToken); independent of the authorization-server PR. No DPoP-capable MCP SDK exists yet, so correctness rests on RFC vectors + an independent verifier + the fixtures. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
- Refresh the held DPoP nonce from every response's DPoP-Nonce header (RFC 9449 §8.2 newest-wins) instead of capturing it once, so a server that rotates or single-uses its nonce no longer turns the negative probes into false "not testable" failures (or vacuous passes). (#1) - Widen the stale iat probe to -303 s (matching the future side) so the ±1 s quantization of the whole-second Date header can't pull it onto the ±300 s boundary and be false-accepted. (#2) - Update the isNonceChallenge comment and the untestable message: probes now carry the held nonce, so a use_dpop_nonce challenge is about the nonce lifetime (rotated/stale/single-use), not a missing nonce. (#3) - Fixture: parse integer env vars NaN-safely (intEnv helper) so a malformed DPOP_CLOCK_OFFSET_SECONDS / DPOP_IAT_SKEW_SECONDS falls back to its default instead of silently disabling the iat window. (modelcontextprotocol#4) Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
- Soften the heldNonce comment: newest-wins refresh is correct for ROTATING servers; a strict single-use server that re-arms only via challenges can still push alternate negatives to untestable (correctly reported, not mis-scored) — the previous "rotate or single-use" over-claimed. (R5) - Fix the clock-skew test comment: the stale probe is now -303s (~273s old), not -301s/~271s. (R5) Comment-only; no behavior change. 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 proof validation (SEP-1932 / RFC 9449) on the MCP 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 #369.
What it tests
That an MCP server correctly validates DPoP proofs presented with an access token (RFC 9449 §4.3). The scenario acts as the client, presenting one valid proof and then a battery of deliberately-broken ones, and checks the server:
htm/htumismatch,iatoutside the acceptance window, wrong token binding, replays — with an appropriate401andWWW-Authenticatechallenge.Server-provided nonces are optional (a SHOULD): if the server issues one, the full nonce flow is exercised; if it doesn't, that check is skipped and the mandatory validation checks still run.
Each check is proven to pass (compliant example server) and to fail (misbehaving example servers), with an automated acceptance suite.
Scope
MCP-server behaviour only. The framework plays the client. The grant type used to obtain the token is irrelevant to how the server validates the proof.
Notes