GHSA-mmpq-5hcv-hf2v

### Impact

The login endpoint response time differs measurably depending on whether the submitted username or email exists in the database. When a user is not found, the server responds immediately. When a user exists but the password is wrong, a bcrypt comparison runs first, adding significant latency. This timing difference allows an unauthenticated attacker to enumerate valid usernames.

### Patches

A dummy bcrypt comparison is now performed when no user is found, normalizing response timing regardless of user existence. Additionally, accounts without a stored password (e.g. OAuth-only) now also run a dummy comparison to prevent the same timing oracle.

### Workarounds

Configure rate limiting on the login endpoint to slow automated enumeration. This reduces throughput but does not eliminate the timing signal for individual requests.