The beta version of 11.3 seems to offer significantly more than previously thought. It has now been discovered that Apple apparently develops a single sign-on service for the Web.
iOS 11.3 seems to include so many new features that you're fine and like to call it iOS 12. Parents should be able to approve Face ID purchases when using an iPhone X. Apple Books is also planned to overhaul Apple's new single sign-up service. On-service for the Web, which may already be introduced with iOS 11.3.
The new component called SecureChannel indicates that Apple is working on a solution that it Benu enables them to log in to websites using their Apple ID. Strings found in SecureChannel show that a web site using this authentication method can access the user's personal iCloud data. Presumably, this only applies to the name and e-mail address of the user. Another benefit for Apple ID users would be the ability to sign in to third-party Web sites without having to worry about creating a new user and password.
This functionality is somewhat similar to single sign-on Apple TV feature that allows users to seamlessly log in to various TV applications after logging in for the first time.
There is also a component that allows users to scan a QR code when scanning asks with the camera application for the Apple ID authentication. What the exact purpose of this system is can not be foreseen.