I have several suggestions :
- if the "target" architecture wont be a windows one ; why dont you use directly the same architecture for your development ? Thus you will avoid to loose a lot of time to try to compile this dll on your computer, wont you ?
- if the target is windows, may be you could check all the existing PHP OAuth classes provided here and there for example :
- https://github.com/abraham/twitteroauth
- http://framework.zend.com/manual/en/zend.oauth.introduction.html
Hope this could help
Regards