Identify player by his smartphone ?

No, what i want is to have the player ID to record him on my own database, so i can sort my players data by their ID. And when they connect, they recover their own data. Like a save/load system but player’s information would be store on a server, but to do such a thing, you need a whole authentification system, with password, which is pretty hard to setup. So i want to get rid of that and recognize the player by his ID. He must have one since it is possible to do online purchase, the player must have an ID i guess