This is the original reference implementation of OAuth in php, imported to git using git-svn from https://code.google.com/p/oauth:
git svn clone https://oauth.googlecode.com/svn/code/ cd code git filter-branch --subdirectory-filter php -- --all
And then used the process described at https://help.github.com/articles/changing-author-info/ to rename the authors (myself, fangel and bpedro) to the email addresses used on their github profiles.
This project is un-maintained, the last maintainer was https://github.com/fangel and the original author was https://github.com/termie
Feel free to fork at will, there are quite a few implementations out there at this point, a few more won't hurt :)