The Web Authorization (OAuth) protocol allows a user to grant a third-party Web site or application access to the user's protected resources, without necessarily revealing their long-term credentials, or even their identity.

As the web grows, more and more sites rely on distributed services and cloud computing or a third-party application utilizing APIs from multiple services.
OAuth 2 is widely used from major internet players (as Google, Facebook, Twitter) in order to secure their (also REST) APIs.

This talk will introduce the OAuth 2 framework and Apache Oltu (OAuth protocol implementation in Java). It will also show how to best use OAuth 2.0 in order to avoid security pitfalls and common mistakes.
http://www.jug.ch/html/events/2015/oauth_hacks.html