authentication agent for PolicyKit

 PolicyKit-gnome provides a D-Bus session bus service that is used to
 bring up authentication dialogs used for obtaining privileges.
 .
 This implementation was originally designed for GNOME 2, but most
 GNOME-based desktop environments, including GNOME 3, GNOME Flashback,
 and MATE, have their own built-in PolicyKit agents and no longer use
 this one. The remaining users of this implementation are Cinnamon, XFCE
 and Unity.