The backend auth for opt-in username/password mode (security.require_login, default
off → zero change; the launch PIN + picker behave exactly as today).
- core/security/login_gate.py: pure gate (mirrors launch_lock) — when login mode is
on, an unauthenticated session reaches only the page shell, /api/auth/login,
/api/auth/logout, /api/profiles/current, /api/setup/status, and the key-authed
/api/v1 API. Deliberately does NOT expose the profile list pre-auth (you type your
name, not pick from a roster).
- _enforce_login before_request enforces it; _enforce_launch_pin no-ops when login
mode is on (login replaces the shared PIN, per design).
- POST /api/auth/login (username = profile name, case-insensitive; brute-force
limited per IP; generic error so names don't leak) + POST /api/auth/logout.
- Anti-lockout: the settings save refuses to turn ON login mode until the admin
account has a password.
Tests: gate blocks→login→access→logout→blocked; case-insensitive username; wrong
password / passwordless profile / unknown user all 401 generically; login list not
exposed pre-auth; can't enable login without an admin password. 12 tests pass. Next:
the login screen + set-password UI + the toggle (increment 3).
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