Oauth it seems tricky, to help me understand I've attempted to code up an example which allows users to log into a php app with their twitter credentials.
The code has been pushed to a branch of my abandonware repo as I don't plan to make on any future changes, checkout README.md for some info on how the code works.
https://github.com/linickx/a/tree/oauth
I found it quite difficult to find some simple code to do this, so hopefully \^that\^ will help someone else :)