Commit 4cda61a1 added support for pre-authenticated logins in
oVirt environments. This feature prevents a user from having
to type their password twice (once to the oVirt management machine,
and then immediately again in the provisioned guest running gnome-shell).
That feature is currently oVirt specific, but a similar feature would
be useful in non-oVirt based virt farm environments.
Toward that end, this commit generalizes the various aspects of the
oVirt integration code, so that it can be reused in a subsequent
commit for adding single sign on support in vmware deployments, too.
Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/1983
