The access-token endpoint accepted unlimited password attempts; the
only existing rate limiters are single-instance helpers for outbound
site requests. Add app/application/security/throttle.py, an in-memory
LoginThrottle keyed by (client address, normalized username) that locks
for 30s after five consecutive failures and doubles the lockout up to
15 minutes. The endpoint answers 429 with Retry-After while locked,
counts only real credential failures (an MFA challenge after a correct
password does not count), and clears the record on success.
X-Forwarded-For is deliberately not trusted because there is no
trusted-proxy setting; behind the bundled nginx all requests share one
address, so the key degrades to per-username throttling, which is the
dimension brute-force protection needs. Sync the dependency snapshot
and architecture metrics for the new module.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
