- app asks only for an email address on the login screen. If logout control is used, this is the only accessible screen.
- upon entry, app stores the email locally and sends it and OS ID (identifierForVendor) to server to confirm valid login. (whenever app is "fresh" (re-loaded after being cleared from memory) it does this again using stored email.)
- server checks email and OS ID against user store
if match:
- server confirms login and app continues
if no match for email:
- server rejects email