The Google+ platform has a API for retrieving Google+ profiles by ID, documented here.
The problem is I am using Google Cloud Endpoint with its built in authentication which returns the authenticated user as a com.google.appengine.api.users.User object, documented here. The com.google.appengine.api.users.User user ID is not the same as the Google+ Profile user ID. Quite unfortunate.
What I am looking for is a work around. A way to either recieve the Google+ profile user ID with Google Cloud Endpoint's built in authentication, or use the Google account user ID to get a users corresponding Google+ profile ID.