How to do it: user identification

Hello.

I'm doing a big game. Off-line multilayer strategy.
In the assumption a lot of players, you log in, you issue commands, go out, the game goes on still.

Is there any environment / server / paid (or not) service,
which would remove the player's identification from me. Ie. the player logs in to this server, is there verified, and to the map with the game is already verified?

Greetings,
Kajetan

 

PlayFab is great. They were recently bought by Microsoft.