AutoLogonUser interprets source as the contents of the gdm3 custom.conf file, and parses it to look for an auto login user, and returns it if found, otherwise it returns the empty string.

InteractiveUsername attempts to determine which single user is currently logged into a gnome3 desktop session.

SetAutoLogin interprets source as the contents of the gdm3 custom.conf file, and returns an updated version of it with the automatic desktop login enabled for the user specified by username.