Hello,

Wanted to work on Guix's website but fate led me to try my way on a
lightdm service...
So, here is what I got for now.
It fails to start a window manager but I don't think I'll be able to
debug the last mile with my sole knowledge.

Beside that, here is a list of possible improvements before merging:

* lightdm-greeter-gtk configuration is a part of lightdm's service.
It might be a good idea to give it its own service but it would
mean we need to write a service for each lightdm greeter.

* lightdm complains about the lack of
  org.freedesktop.DisplayManager.AccountsService interface.
  The lightdm package provides the relevent files but it seems
  accountsservice doesn't find them. I think it searches them in
  $XDG_DATA_DIRS/accountservices . See
  https://github.com/NixOS/nixpkgs/issues/45059

* lightdm-gtk-greeter's wrapper is handmade and ugly.

* General refining.

A thorough review would also be welcome as I'm not really sure I know
what I'm doing.

Thanks!

L  p R n  d n