Couple of questions:
(1) If ga_login is enabled for a user, iiuc, it's required. What happens if the Google service site is unavailable? Can I still somehow login?
(2) Can I enable ga_login only for certain users/roles? E.g., 'normal' users can login to their accounts with just the usual password, but "admin role" users also have to, or instead, provide the GA code?