Read MAC address of a bluetooth device connected to arduino

I want to secure the access because I will use the arduino to open a door, first security is change the bluetooth pair code, the second one is filtrate which android device can open it.

I need to know which device is connected, if I have this in the sketck I don't care if you run my android app and know the bluetooth pair code.

Maybe saving in a var the devices previously scanned with AT+FSAD=?

Thanks for docs!