The GUID of the peer performing the role of server when authenticating.
If you are constructing a DBusConnection and pass g_dbus_connection_flags_authentication_server in the flags property then you MUST also set this property to a valid guid.
If you are constructing a DBusConnection and pass g_dbus_connection_flags_authentication_client in the flags property you will be able to read the GUID of the other peer here after the connection has been successfully initialized.