fix(auth): make grant expiry exact, dropping the clock-skew grace

[kixelated]

Maintainer decisions

• Maintainer decision: expiry is exact; the asymmetric 5s grace is removed.
• JWT exp is refused at exp == now in Rust, matching JS

#3774 added CLOCK_SKEW (5s) to moq-auth, and #4237's Grant::deadline() reused it. The grace was asymmetric: a grant expiring in 1s got 1s, but one that expired 1s ago got 4s more. Now a grant whose expires is at or before now is refused with GrantExpired, and deadline() is now + remaining, or now once passed.

Changes

• rs/moq-auth/src/grant.rs: delete CLOCK_SKEW and the until helper; validate compares expires <= now, deadline() uses duration_since(now).unwrap_or_default().
• Tests (paused Tokio clock): validate refuses an expiry of now and of 1s ago; deadline() is at most the expiry and a past one is now; the client refuses an expired grant at connect and closes a live one at its expiry (within 1ms of timer resolution); the relay's fixed lease of an expired grant ends at once.
• rs/moq-auth/src/key.rs: Key::verify refuses a JWT when exp <= now (was exp < now), matching jose. nbf already agreed (refused only when nbf > now, as jose does). The checks move into a private validate_times(claims, now) so validate_times_at_the_boundary tests both edges at a fixed instant; it fails without the fix.
• Docs: doc/bin/relay/auth.md, doc/lib/rs/moq-auth.md.

Impact

• Public API: none. CLOCK_SKEW was pub(crate); Grant::validate and Grant::deadline keep their signatures.
• Behavior: an auth server whose clock runs behind the relay's no longer gets up to 5s of grace. A grant already expired on arrival is refused at connect and treated as Invalid on revalidate; a fixed lease with a past expiry ends immediately. A JWT is refused at its exact exp second in Rust, as it already was in JS.
• Wire: none.

Notes

• JS (js/auth) never applied a grace to grant expires (the GrantSchema checks shape only), so nothing to change there.
• JWT exp/nbf validation never shared CLOCK_SKEW and has no leeway in either language. There is no separate js/token package; JS verifies through jose in js/auth, and Rust and JS now agree on both boundaries.

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[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-28T19:02:15.189578Z	79e5af8	New commits

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[kixelated]

MERGE — Dropping the asymmetric 5s clock-skew grace makes grant expiry exact and is a clear net win.

Positive improvement

The old until() helper was asymmetric and easy to misread: a grant with 1s left kept 1s, but one that expired 1s ago still got ~4s. validate now refuses expires <= now, and deadline() is now + remaining (or now once past). That matches the maintainer decision in the PR body, aligns Rust with JS (js/auth never applied grace), and removes a footgun without changing public signatures (CLOCK_SKEW was pub(crate)).

Worth the complexity

Complexity goes down, not up: constant + helper deleted, comparison is a single <=, docs say “keep the auth server's clock in sync.” The interoperability risk is real only for auth servers with bad NTP; papering that over with a hidden 5s grace was the worse trade. JWT exp/nbf stays untouched (correct scope).

Approach

Exact expiry is the right call here over a configurable leeway. Tests cover the important edges with a paused Tokio clock: refuse at now and 1s ago, deadline() not past the expiry / past → now, client refuse-at-connect and close-at-expiry (±1ms), relay fixed lease of an expired grant ends immediately. Docs in doc/bin/relay/auth.md and doc/lib/rs/moq-auth.md match the code.

Minor note (not blocking): Rust JWT still accepts at exact exp (exp < now) while grant validation uses <=; the PR already calls that out. Fine to leave for a follow-up if you ever want one policy everywhere.

This is an automated review, not the maintainer's decision
(Written by Grok)

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• rs/moq-relay/src/auth.rs

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Walkthrough

Grant validation now rejects grants that expire at or before the current time. Past grant deadlines map to the current instant. Client and relay tests cover expired-grant rejection and lease closure at expiry. Token verification now rejects tokens at their expiration time. The documentation describes expiry without a clock-skew grace period.

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 65666

Expiry enforcement appears consistent, but the client expiry test can fail when connection setup is slow. The PR is mergeable with this test-timing issue addressed or explicitly accepted.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 65666

Expiry enforcement is tighter overall, but a narrow renewal-timing race may allow a session to remain open after its previous grant expires. No confirmed security finding or broader boundary bypass was identified.

Retained concerns

• Low · security · inferred: A successful revalidation ready at the previous grant’s expiry can replace its deadline before the client driver or relay lease takes the expiry branch, weakening exact-expiry enforcement for that session.

Security review details

Security Blast Radius

• inferred — The possible renewal-ordering gap affects a session whose expiry and successful revalidation coincide. Each refreshed grant must still pass the auth client’s validation; the available evidence does not establish token forgery or an expanded privilege boundary.

Trust Boundaries and Controls

• observed — Signature decoding precedes token time and scope checks. Grant responses are validated before admission, and relay revalidation checks the refreshed grant against the session’s existing identity and coverage before updating its deadline.

Resilience and Maintainability Implications

• observed — A stalled revalidation reply does not prevent the client driver from polling expiry. The unresolved case is a successful reply ready when expiry is also ready.

Hardening Proposals

• proposed — Before applying a refreshed grant, explicitly resolve whether the previous deadline has passed in both the client driver and relay lease; exercise simultaneous reply-and-expiry readiness in tests.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 94.12% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 4 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: exact grant expiry with removal of the clock-skew grace.
Description check	✅ Passed	The description directly explains the expiry behavior, implementation changes, tests, documentation updates, and impact.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @rs/moq-auth/src/client.rs:
- Line 514: In the test around the `client.connect(request())` call, compute the
Tokio deadline `at` from `expires` before connecting, using the remaining
duration at that point. Remove the post-connect deadline calculation so
connection time cannot shift the expected expiration deadline.

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[chatgpt-codex-connector]

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Reviewed commit: 6566630bb5

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[chatgpt-codex-connector]

Inject a controllable wall clock into the expiry test

This test pauses only Tokio's monotonic clock, while SystemTime::now() continues using real wall time. If a loaded CI runner spends the short 2–3 second expiry window starting the loopback server, or if the host clock is adjusted, duration_since(...).unwrap() can panic or connect can reject the grant before the timing assertions, making the regression test nondeterministic. Use an injected/mock wall-time source rather than a real near-future timestamp.

AGENTS.md reference: AGENTS.md:L19-L19

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[kixelated]

Fixed in 79e5af8 without injecting a clock. The wall clock is read inside Client::connect (via Grant::deadline()), so a mock would need a clock parameter on the public Client or Grant API. The test instead follows the existing auth test pattern: paused Tokio clock, real SystemTime for expires. The expiry is now an hour out, so a loaded runner cannot expire the grant before connect answers. The expected deadline is bounded by wall and Tokio readings taken before and after connect, so the assertions no longer depend on how long setup takes. It still fails if a grace is reintroduced (checked with +1s on deadline()). The exact boundaries themselves are covered by the fixed-instant validate_times_at_the_boundary.

(Written by Opus 5.5)

[kixelated]

Merge summary:

• Merged main in (no conflicts; fix(auth): admit a SETUP token equal to the jwt query #4359 and fix(cli): refuse a client CA under --auth-public on a listener #4364 auth.md edits combined cleanly).
• Codex P1 and the CodeRabbit minor both concerned a_grant_closes_at_its_expiry. Fixed in 79e5af8: the expiry is an hour out, and the expected deadline is bounded by wall and Tokio readings taken before and after connect, so the result no longer depends on how long setup takes. No clock injection, since the wall clock is read inside Client::connect; see the thread reply. Verified the test still fails with a 1s grace on deadline().
• Kept as decided: expiry is exact (no grace), and a JWT is refused at exp == now.
• just check passes locally, CI is green, and Codex gave 79e5af8 a thumbs up.

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