Well, well. A little update (actually, a pretty big one) for anyone keeping tabs on this.
I've just added some new features into the API, as well as fixing a bug in the previous version.
It now has complete functionality for:
Authorizing a User
Scores for Guests and Users
Data Storage (globally for the game, or for a particular user)
There's also plans on implementing status updates (to tell Game Jolt that the user is playing their game) and pulling user information in from Game Jolt.