Logging in using facebook/twitter account

I am developing an iPhone application, which has a registration feature as well. Now, I would like开发者_JAVA百科 to enable those users who already have account with facebook or twitter to login directly using their FB/Twitter credentials.

Pl. help me with this.

Here is the SDK for facebook connect for the iPhone: Facebook iPhone SDK

For Twitter, you could try this? MGTwitterEngine

Twitter's offering is called Sign in with Twitter, and Facebook offers Login with Facebook.

These links should get you started.