You are not supposed to do this. They metioned this in the last WWDC.
GKCloudPlayer is only for, to be used for Sessions. It basically has
two pieces of data, a player ID that is unique to your app as well as
the display name, that is what the user will have as what they want
they name to be displayed. This is not a GKPlayer object at all.
If you try to use this for a leaderboard, for achievements, for other
multiplayer, for anything else, it will not work. So please don't do
that.
Everyone will be very disappointed. So how do we get our Cloud
Players? Basically you can get your current signed in player.
Most of the things in Sessions basically are going to be called from
your current player though there's not a whole lot of need to make
sure that you have the player, that you are then saying, "Oh, this
player is saving this data." All that's handled for you in the
background.
https://developer.apple.com/videos/play/wwdc2016-611/?time=1139