Screen Off can be used to turn off and lock the screen of any Android 6.0 (Marshmallow) or heigher device in a way that it can be unlocked without violating the security policy that requires a PIN to unlock.

That means that you can use your fingerprint to unlock your device as you would normally do if the screen was turned of by pressing the hardware power key.

Screen Off can also be assigned to be the Assist App of your device and thus it can be activated by long-pressing the Home key.

It is distributed as Free Open Source Software and its source code is available at https://github.com/jsalatas/ScreenOff