How to integrate log-in credential

Thanks for previous replies,

i am doing mobile application with user log-in, i am maintaining separate database to handle the user log-in details. i want to integrate the facebook and twitter user log-in into my application.(ie) if user having facebook or twitter id, if they use that id to access my application it should be accessible.for example in our stack overflow log in we having different log-in category(facebook,Google). Can anyone guide me how to do this in our own application. I very much eager to learn this kind of knowledge, if i made anything wrong pls let me know.

---