Open Radar

 
As applications for the AppleTV often rely on CloudKit for data storage, which is tied to the user's Apple ID, we need a way to allow users to easily switch the active iCloud account on the device.

An example: I sell an app that lets users save videos to watch later, which uses CloudKit to store that data. If multiple users have the apps on their phones in the same household, only one of those users can practicably use the ATV app. If the other user wants to see their data on the ATV app, they have to log out the other user in the Settings app, and then log in as themselves.

If there were a way to let ATV users register multiple iCloud accounts, and then let developers provide a way to let users select the desired account... 

Unlike an iPhone, an AppleTV is a shared household resource. There needs to be a way to let users access their accounts on it

Steps to Reproduce:
1. Use a CloudKit powered app with AppleTV
2. Second person in same household uses the same app.
3. Second person can't use the ATV app!

Expected Results:
All users in a home could use the same ATV app.

Actual Results:
Only one person in the home can use the app.