Add an opt-in "remember this device" at the second-factor step. On opt-in
a random token is minted, set in an httpOnly+Secure+SameSite=Strict cookie,
and only its HMAC hash is stored in a new TrustedDevice table. A later sign-in
from the same browser still requires the password (factor 1); a matching,
unexpired trusted device lets the login skip factor 2 only.
The token is never accepted for step-up — a trusted-device login does not stamp
mfaVerifiedAt — so a stolen device cookie cannot reach a destructive action.
Trusted devices are listed and revocable from the security surface, are revoked
wholesale when the second factor is removed or the user signs out everywhere,
and cascade away on account deletion. A recovery-code login never trusts the
browser. Migration 0204 adds the table (and the instance-wide mfa_required
policy column that the enforcement work reads).
Reject any challenge that is not a login challenge before minting a session,
cap the disable and confirm request bodies through safeJson, and correct the
recovery-code scan comment to match its early-return-on-match behaviour.
When a password is accepted for an account with a confirmed TOTP factor, the
login route no longer mints a session or token. It creates a single-use,
~5-minute MfaChallenge (the opaque ticket is stored only as a hash) and
returns HTTP 200 with data:null, error:null and meta.mfaRequired + mfaTicket +
methods. The client completes the login at POST /api/auth/mfa/verify with the
ticket + a TOTP or recovery code, receiving the exact same token bundle the
password path issues, with the session stamped second-factor-verified.
- The ticket is claimed once, atomically, only after the factor verifies, so
two concurrent submissions can mint at most one session; no session ever
exists before factor two.
- Wrong codes increment the ticket attempt counter and burn it at the cap
(throttle, not an account lock); the anonymous verify surface is also
rate-limited per IP.
- meta.mfaRequired is returned only after a valid password and the
invalid-credentials response is identical regardless of MFA state, so an
attacker without the password cannot enumerate MFA.
- The session/token tail is extracted to login-response.ts and shared by both
the password path and the verify path, keeping the transport contract
identical. OpenAPI registers the verify endpoint, the MFA management
endpoints, and the mfaRequired login variant.
Marc-André Bombeck