PHPMaster.com has posted the first part of a new series they're presenting on working with OAuth in PHP, specifically using it to connect to the Twitter API. This first part of the series introduces you to the concepts of OAuth and some early code to work with user credentials.
A common complaint about OAuth is that it is very difficult to understand, but perhaps some of that confusion is because of an expectation that the abstraction provided by a third-party library will erase the need to understand the steps of an OAuth transaction - it does not. This two-part article demonstrates how OAuth v1 works by explaining the process of connecting a PHP application to the Twitter API using only a few built-in functions to post a message to a user's Twitter stream.
The process is broken up into two steps - first you'll need to set up the request credentials so your application can connect to the Twitter service (as created here) then use that connection to fetch the rest of the necessary credentials (three total: Consumer, Request and Access Credentials). Cut and pasteable code is provided.