Play Games Services for Web - Turn based Game - Creating and Joining room in Javascript

I created a Simple Web Board game, where each user takes a turn and make their move.

I am now trying to integrate Google Game Play Services to connect 2 friends and let them compete.

With reference to http://ift.tt/1Ou3noo

While creating a match, I am to pass invitedPlayerIds, which will be the player ID of my friend. But how will I get the ID of the friend, who is logged into his own device?

I was checking this Rooms API @ http://ift.tt/1T64QJM

Seems most methods are only for Internal use. We can't create, list and join rooms.

Please advice me on how to proceed?