"login" has "auth sufficient pam_self.so" but a screen locker is
supposed to ask for password regardless.

pam_unix(8) requires root priveleges to access master.passwd(5),
so try authenticating via setuid helper first.

--- pam/gtklock.orig	2023-05-06 13:44:22 UTC
+++ pam/gtklock
@@ -1 +1 @@
-auth include login
+auth include unix-selfauth