The SitePoint PHP & MySQL tutorials blog has posted the second part of their series looking at authenticating your applications against the Twitter OAuth method. You can find part one here.

In Part 2, we're going to walk through how to let users log in to your site using Twitter's "Sign in with Twitter" authentication technique. This in turn will give us access to Twitter's API. You may have noticed "Sign in with x" buttons becoming increasingly popular as the number of username and password combinations we're asked to remember seems to increase at an exponential rate. The idea of a single login is by no means a new one.

They walk you through the process - registering your application and, using the TwitterOAuth library, create a login page that sends the information to the OAuth servers and, if valid, calls a callback script on your site.