We never quit the main loop, but if something odd happens that causes it
to quit outside our control, ensure that we don't return the "auth
success" status code.
Changes the auth failed label into an auth status label, and prints a
dot once every half second while authenticating.
Also reduces the post-auth-failed pause to 1 second; 2 seconds is longer
than it seems.
By default it'll look at your environment to try to figure out which
display manager is used in order to start a new session. We first try
the org.freedesktop.DisplayManager dbus interface, and if that fails,
inspect XDG_SESSION_DESKTOP to try to figure out which display manager
is running.
The user can also still specify the correct display manager, or a custom
command.
This includes an abortive attempt to do a gtk4 dialog (which I don't
think is possible, as gtk4 doesn't allow embedding toplevels anymore),
and an iced dialog, which I just never started writing.
