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).
When a password is accepted for an account with a second factor, the
login response carries a single-use ticket instead of a session. The
login page now renders a second step: a TOTP or recovery code, or a
WebAuthn security-key assertion scoped to the account's registered keys.
A WebAuthn-only account (no TOTP) is recognised at the password step and
offered the security-key path.
The security-key verify endpoints validate the open ticket, verify the
assertion against the user's second-factor credentials, and only then
mint the session through the shared login tail, so no session exists
before the factor passes. The login page also arms passkey conditional-UI
autofill on the username field.
Marc-André Bombeck