Old authenticators won't work

The previous authenticator system (before #218) doesn't set `session.authenticated` anymore. Previously the session object automatically returned `authenticated = True` when `login_data` is set. This was removed in 359d9c7946289444f8a0e9dfa09868705427cb3e, therefore subsequent handlers will treat the session as non-authenticated resulting in '5.7.0 Authentication required' errors.