So, i'm coding a minecraft launcher which contains a cheat, and this cheat is commerciable, so i want to perm only the persons who bought the client access it.

I pretend to do this adding a whitelist in my launcher.bat/launcher.jar , so when a person launch it, it will check if this nickname is on my whitelist, if yes then proceed to the intializing, if not, automatically closes and send a message like "Insufficient permissions."

Does anyone knows how to do this? If i need to use a .xml with the nicks idk