My launchd plist now:

Hi, I was able to get it working by using "WatchPaths". For watchPaths to work the file need to be existing already. When the button was clicked I wrote to a file and my App would be launched because the file was modified. But my app stands behind the authorisation plugin window. It comes in front once clicked. I am able to toggle between windows. But it would be nice if I could have my app displayed in front. Can this be done ? Also the app is launched only when logged out. Is it possible to display the app even when locked and not only logged out?

Thanks @eskimo for the reply. Thanks for confirming that pre-login agents is the way to go. Right now the GUI app is showing up all the time at logout. How can I get it to work when only the button on the authorisation plugin is clicked? I tried WatchPaths and QueueDirectories, when the button is clicked I created a file in the WatchPath directory so the launchd launches the app only when there is a file in the directory(according to the definition of WatchPaths/QueuDirectories). But that did not help. The GUI app is showing up irrespective of the file being there or not in the WatchPath folder.

Yes as an Authorisation plugin

thanks in advance