I've been working with OAuth, as a provider and consumer, and there isn't a lot of documentation around it for PHP at the moment so I'm sharing my experience in this series of articles. This relates to the stable OAuth 1.0a spec, however OAuth2 has already started to be adopted (and differs greatly). This article uses the pecl_oauth extension and builds on Rasmus' OAuth Provider post.
OAuth Pages and Endpoints
OAuth has a little more baggage with it than just passing a username and password to an API. As well as your standard service endpoint you will need: