App persistence for Android and iOS
The most popular way to store user data in iOS is to use BubbleWrap's App::Persistence vis a vis
App::Persistence["username"] = "firstname.lastname@example.org"
Unfortunately Bubblewrap comes with a LOT of extra bells and whistles you may not need, and no Android support that you do need.
With the help of @markrickert, and using @darin 's JSON serializer, you have one syntax to rule them all.