Ryan Boyd

A very good overview of OAuth, its use cases and implementation examples in PHP and JavaScript. (C# or some .NET language should have been used, at least some of the time, IMO.) There is also a useful chapter on OpenID Connection. I think the overview of authentication vs. authorization is good for anyone considering API Security models.

Very succinct and understandable description of the basic information flows in OAuth. The author gives source code in PHP and Javascript for all the essential parts which are necessary to access an API via OAuth.

There is also a chapter on "Mobile apps" and one on "OpenID" which I find somehow incomplete and not so well to understand.