Facebook logging a user with manual with access token

I happened across this, but i don’t understand how to call this method manually from the restivus API… any ideas, how do I manually log a user in with the facebook user’s access token,

This is common to any IOS native developer using Meteor for a backend, and since facebook authentication is managed by the team core, should be built in the core. Especially, since this is kind of complicated, IMHO.

Any ideas.