add yubikey signin

modules/desktop/greetd/default.nix

@@ -17,6 +17,9 @@
     };
   };
 
+  # allow yubikey signin with u2f
+  security.pam.services.greetd.u2fAuth = true;
+
   # ensure the user exists
   users.users.greeter = {
     isSystemUser = true;