Sanjeev Dwivedi posts the details:
Today, we are excited to announce that on Windows Store apps and Windows Phone 8 apps, you can easily integrate Facebook Login. Facebook Login lets users sign in to Facebook only one time across multiple devices. If another app then wants to access the users Facebook account, the user just provides consent and doesn’t sign in again.
Follow the straightforward procedure laid out by Sanjeev and get Facebook authentication in your Windows Store apps (and Windows Phone apps) today. [more]