Hi Ravi,
You need to roll your own implementation on this one. I would suggest having a look at the Liferay source code to understand how they do it for Facebook and the duplicating the efforts for Twitter and LinkedIn -- at least that is what I had to do a few years back on 6.1. There are plenty of frameworks out there that will make it easy to integrate with the 3rd parties, once you have your custom auto login and authenticators in place in the portal.
