There's some interesting things going on behind the scenes here. Some of this will find it's way back to shindig.
In any case it's a generalized solution for calling JSON-RPC endpoints with postMessage flow using OAuth2.
Originally shared by Mano Marks
Pretty cool, a new way to access many of Google's APIs, though not Maps at the moment. In particular, Google+, Freebase, Contacts, Latitude, and a host of other APIs. And it'll handle the authentication for you.

Very nice! Going to dig through their postmessage code, that's always the painful part.
Jakob Heuser , Dec 01 2011 on known.dev.inuus.com