Detect invalid auth

[shilangyu]

Invalid auth tokens will in many cases cause infinite spinners. Since invalid authentication always means invalid tokens, it is safe to log the user out or mark the account as needed for re-login.

[dessalines]

On the front end, we handle this like:

    if (msg.error) {
      if (msg.error == "not_logged_in") {
        UserService.Instance.logout();
        location.reload();
      }