Android P (beta) has it in system settings. I am using it right now. (Although I have no idea how to test if it's really working) There's also this interesting

Android P (beta) has it in system settings. I am using it right now. (Although I have no idea how to test if it's really working) There's also this interesting app: https://play.google.com/store/apps/details?id=app.intra https://play.google.com/store/apps/details?id=app.intra