I'm please to say that the latest pre-release developer library includes some App Transport Security docs. This documentation matches the implementation you'll find in the beta 2 releases.
As always, if you find anything incorrect or unclear, please file a bug against the docs and then post the bug number here, just for the record.
Share and Enjoy
—
Quinn "The Eskimo!"
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1@apple.com"