Client side login


I noticed a site today that had a ‘login with twitter’ button on the main page. I would like to be able to allow users the option to log into the site via their twitter account. I was reading up on the API and its functions and was curious if anyone had actually built an app for this specific function? I understand its actually a simple thing to use the oauth codes and posts however, I do not have the ‘time’ to attempt to build an app unless its absolutely needed (I dread having to code everything) and thought i would ask before diving head first into lines of code.