perf: cache OIDC verification keys in k8sjwt#391
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July 4, 2026 05:05
| flight singleflight.Group | ||
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| mu sync.Mutex | ||
| issuers map[string]*issuerKeys |
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Is it a concern that we could end up with a lot of entries cached over time? Do we need to proactively clear out old entries at all?
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good point, the eviction for issuer should be bounded by the config now (the expected issuer), but there could be a real gap - revoked keys never aged out and added a 5-minute max-age so revoked keys stop being trusted within one interval, PTAL.
Previously every k8sjwt.Verify call performed a full OIDC discovery (two HTTP round trips: the discovery document plus the JWKS) against the issuer. In JWT auth mode that cost was paid on every authenticated RPC, and MintJWT paid it again for the client token. Introduce k8sjwt.CachedVerifier, which caches each issuer's verification keys in memory: - Keys are fetched on first use and refetched synchronously when a JWT presents an unknown keyID (key rotation). Since that keyID comes from an unverified token, refetches are rate-limited to one per issuer per 10s so bogus keyIDs cannot force a fetch storm, and concurrent misses are coalesced with singleflight. - Cached keys older than 5m trigger an asynchronous refresh so keys removed from the JWKS (revoked) age out; requests are served from the current cache while the fetch runs (stale-while-revalidate). - The issuers map is bounded by the configured trusted issuers: Verify rejects other issuers before consulting the cache. The auth interceptor and the session-identity service share one CachedVerifier. The package-level Verify remains as an uncached one-shot wrapper.
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Previously every
k8sjwt.Verifycall performed a full OIDC discovery (two HTTP round trips: the discovery document plus the JWKS) against the issuer. In JWT auth mode that cost was paid on every authenticated RPC, and MintJWT paid it again for the client token.Introduce
k8sjwt.Verifier, which caches each issuer's verification keys in memory. Keys are only refetched when a JWT presents an unknown key ID (i.e. on key rotation). Since the triggering key ID comes from an unverified token, refetches are rate-limited to one per issuer per 10s so bogus key IDs cannot force a fetch storm, and concurrent misses are coalesced withsingleflight. The auth interceptor and the session-identity service share one Verifier.