Zend Framework has pretty good OAuth consumer implementation. However, it has no support for implementing OAuth provider, and it turns out that there aren’t many other libraries for it. Most examples out there base on PECL oauth extension, which works just fine, with one caveat – you have to have this PECL extension installed, while ZF implementation does not require that.
So I went ahead and wrote some code that allows to easily add OAuth provider to your ZF-based or ZF-using application. That should make writing OAuth provider easier.
Note that the code does not implement the whole server – just the OAuth protocol wrapper, you’d still have to do all the work of managing tokens/keys/nonces by yourself. See example server in the repository and the wiki on github for more details on how to do it, but the protocol follows what PECL oauth does pretty closely, so many tutorials for it would be mostly applicable to this one too.
Check out Zend_Oauth_Provider on github, if you want to improve it – please fork and submit pull requests.