Client Auth: DPoP Sender-Constrained Tokens (SEP-1932)#394
Open
PieterKas wants to merge 5 commits into
Open
Conversation
…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>
This was referenced Jul 7, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Overview
Conformance tests for DPoP sender-constrained tokens (SEP-1932 / RFC 9449) on the MCP client side.
This is the first of three DPoP PRs (client, MCP server, authorization server) and the shared foundation: it introduces the DPoP-capable test authorization server and the resource-side proof "judge" that the server and authorization-server PRs reuse. Please review this one first.
Closes #368.
What it tests
That an MCP client correctly obtains and presents a DPoP-bound access token:
DPoPscheme, notBearer.jti).Because server-provided nonces are optional in RFC 9449, the scenario runs in two postures:
auth/dpop— the common nonce-less baseline.auth/dpop-nonce— the authorization server and MCP server both require a nonce (§8/§9), additionally checking that the client retries with the server-supplied nonce.Each check is proven both to pass (compliant example client) and to fail (deliberately-broken example clients), with an automated acceptance suite.
Scope
Client behaviour only. The test authorization server and test MCP server are the judges — they observe and score; they don't exercise their own enforcement here (that's PR #369 / #370).
Notes