Single sign-on makes it easy to enjoy content from many different sources on the Apple TV without entering account information into every app. Participating TV providers automatically log in to every supported app requiring authentication. Single sign-on can also be configured on the iPhone for seamless viewing. Once the feature is set up on the Apple TV, a list of authenticated apps that are available can be accessed.
Noticed the home button on your Apple TV doesn't go to home anymore? Once updated to tvOS 10.1, the default behavior of the home button on Siri Remote changes automatically. Instead of returning to the home screen, the home button opens the TV app. Apple introduced the TV app to help unify all of the different streaming services and media libraries in one place.
FIOS is currently not available as a TV Provider option through Apple's Single Sign-On feature. Signing up through Single Sign-On grants users immediate access to all the apps in their pay TV package on Apple TV, and all supported apps on their iPhone and iPad. This eliminates the need to log in to individual apps using your cable or satellite provider information.
iOS 10.2 and tvOS 10.1 both introduce Apple's Single Sign-On option. The feature allows Apple users to sign in to their cable or satellite-TV provider through their Phone, iPad, iPod touch, or Apple TV. This then allows users to enjoy instant access to supported video apps that their pay TV subscription includes. It also supports the new TV app introduced in iOS 10.2. Apple is always adding new cable and satellite providers to its list of supported carriers. Here's the most updated list:
Updates: List has been last updated on April 20, 2017 (v. 10.3.1)