OpenSocial has been tied to the OAuth specification almost from the start, but it can be pretty confusing to try and figure out the differences between two-legged OAuth, three-legged OAuth, and OAuth request signing -- terms which are all thrown around pretty casually in the OpenSocial documentation.
To help make sense of it all, I've updated the OAuth Use Cases page on the OpenSocial wiki. You'll find additional diagrams and clearer request flows showing how data can be transferred between social networks, users, and third party application servers. Additionally, there are hypothetical examples showing where each type of OAuth comes in handy, as well as some links to container-specific resources for obtaining OAuth keys for your applications.
