Apple today announced Facebook integration for iOS 6 that allows users to sign in once and easily post back to the social network.

Similar to Apple’s Twitter integration, iOS 6 offers the “tap to post” option directly from the notification center, and sharing from Photos, Safari, Maps and other applications. Apple has also added Facebook messages to its address book and Facebook events to its calendar app. The App Store now includes Like buttons so users can see which apps, music, movies and shows their friends Like. Game Center will import friends from Facebook, though it’s unclear whether Game Center Challenges will work for cross-platform Facebook-mobile games.

An Apple-Facebook partnership has been speculated about for years, but past attempts at integration apparently fell through for Apple’s Ping service and iOS 5. Late Apple CEO Steve Jobs called Facebook’s terms “onerous” in the past. Now, either through leadership changes or growing necessity, the companies are apparently able to work together. The integration could help Apple and Facebook as they compete with Google, which offers its own mobile operating system and social network.

Developers could also benefit from the partnership. Facebook single sign-on could reduce the friction associated with connecting third-party mobile apps with a user’s Facebook account, and Like buttons in the App Store could improve app discovery.

Last year Apple brought Twitter integration to iOS 5, which allowed single sign-on for Twitter use on the phone and with any third-party app. Today Apple shared that Twitter has seen a 3x growth increase in iOS users since then.

We will update with more information as it becomes available.

Images from The Verge liveblog from WWDC.

This post is excerpted from an original post on our sister site, Inside Facebook, here.