verify_api_key Argon2-verifies every candidate sharing the 8-char
prefix. With unlimited candidates, an attacker who can provision many
keys against one indexed prefix could force the server into per-request
M×Argon2 — a few hundred concurrent connections trivially DoSes the
manager since the verify runs before any concurrency cap.
Cap the candidate set at MAX_API_KEY_CANDIDATES = 16; log a warn when
truncation kicks in so operators can spot it. With 32-byte random key
bodies the natural collision rate is negligible, so truncation under
benign load shouldn't happen — its presence is the alarm.
Switching the verify hash from Argon2 to SHA-256 (the audit's other
suggested fix) is a larger refactor (new hash column, backfill, dual-
hash verify during migration) and is left for a follow-up.
AUDIT.md anchor: F-S-006 (cap; hash swap deferred).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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