How to do a login with Game Center credentials [Unity]

To make a login with Game Center credentials, we just need to get the Game Center user id and perform a login with this call:

GamedoniaUsers.LoginUserWithGameCenterId ( gcuid, delegate (bool success) {
    if (success) {
        //TODO Your success processing
    }
    else {
//TODO Your fail processing } });

More info here: User management guide