Cluster's Rizwan Sattar has been playing around with Safari View Controller on iOS 9, and he discovered that it can be used as an onboarding tool to make users sign up for web accounts in apps more easily:
In the past I always worried about building a seamless first-time experience for our users. None of the “magic” solutions felt elegant.
Using a hidden Safari View Controller to help identify your user removes user confusion and makes your app feel magical when users use it for the first time.
The videos show how much of a difference using Safari View Controller for authentication in the background makes compared to existing solutions. Even if the background method used by Sattar stopped working, the automatic login and dismissal flow (second video) seems magic compared to shared web credentials with iCloud Keychain, which is already very useful (I love it, for instance, in Junecloud's Deliveries). Yet another reason why we should keep an eye on Safari View Controller and hope it'll be widely adopted on iOS 9.