i create a fitness app, but i need to backup savedata as personal activity and exercises, but if i use tiny web db all the smartphone use the same data.
I want that if an user uninstall and reinnstall my app in another device app inventor can automatically read the google account mail, for example pippo@gmail.com and tiny web db can retrive his savedata, because i create a list for example called pippo@gmail.com_exercise1 for one users and jack@gmail.com_exercise1 for another users in another smartphone, but must be automatic, because i don't want that users must write their email address
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my app
https://play.google.com/store/apps/details?id=appinventor.ai_matteo_muucco.fitness_maker
You could model your authentication after the re-entry code system used at code.appinventor.mit.edu, where users' re-entry codes are generated randomly when they connect, unless they provide the re-entry code from their prior sessions.
Each phone could save the re-entry code in TinyDB, for convenience, to save having to re-type it each session.
The re-entry code would have to be used as part of the key of each user's data, in whatever server storage system you use.