/usr/share/polkit-1/rules.d/sddm.rules

polkit.addRule(function(action, subject) {
    if (action.id == "org.kde.kcontrol.kcmsddm.save" &&
        subject.isInGroup("wheel") && subject.active) {
        return polkit.Result.YES;
    }
});

https://projects.kde.org/projects/frameworks/kcoreaddons/repository/revisions/master/entry/src/lib/jobs/kjob.h#L243

the synchronous job->exec() might block, so I just simply change it to asynchronous one:

diff --git a/src/sddmkcm.cpp b/src/sddmkcm.cpp
index be07230..7e56727 100644
--- a/src/sddmkcm.cpp
+++ b/src/sddmkcm.cpp
@@ -83,17 +83,17 @@ void SddmKcm::save()
     saveAction.setArguments(args);
     
     auto job = saveAction.execute();
-    job->exec();
-
-    if (job->error()){
-        qDebug() << "Save Failed";
-        qDebug() << job->errorString();
-        qDebug() << job->errorText();
-    } else {
-        changed(false);
-        qDebug() << "Option saved";
-    }
-    
+    connect(job, &KJob::result, [this](KJob *job){
+                if (job->error()) {
+                    qDebug() << "Save Failed";
+                    qDebug() << job->errorString();
+                    qDebug() << job->errorText();
+                } else {
+                    changed(false);
+                    qDebug() << "Option saved";
+                }
+            });
+    job->start();
 }
 
 void SddmKcm::prepareUi()

Git commit e5e4c3507c20adf9b3d61efaa9c0ef0698919e43 by Leslie Zhai.
Committed on 20/10/2015 at 09:03.
Pushed by lesliezhai into branch 'asynchronous-save'.

Use KJob asynchronous instead of exec()

M  +14   -11   src/sddmkcm.cpp

http://commits.kde.org/sddm-kcm/e5e4c3507c20adf9b3d61efaa9c0ef0698919e43

I believe you pushed it into wrong branch?

Hi Bhushan,

sorry that, Martin told me to upload my patches to http://git.reviewboard.kde.org for review at first, sorry for my mistake ;-(

Hi David && Bhushan,

Could you review this? thanks a lot!
https://git.reviewboard.kde.org/r/125832/