The app token thing is only used in Unity editor, so only in development. This is a work-around, since it was impossible to simulate regular facebook login flow in Unity editor and we wanted devs to be able to test their games in the editor, which is much faster than building and uploading it.
You are not supposed to create your own login process. Just import the sdk package into Unity and open scene InteractiveConsole in Assets\Examples Try building it for iOS/android/canvas, it works on all platforms without any code change necessary
Let me know if have any problems