I want to design a Flutter app that uses Reveneucat as a third-party plugin for subscriptions. Initially, users will be given some free credits, but once they use them up, they will have to subscribe to get more credits. However, I'm not sure how to implement this when using Firebase Auth. Currently, it seems that if a user changes their email account, they can regain the initial credits, rather than having only one account in Firebase, regardless of whether they change their account.
After made some research I found I can get ios udid with device_info_plus: ^9.0.2 and android id with android_id: ^0.3.3. But since firebase auth does not support directly authenticate this uuid, I'm gonna use this id as email and password for firebase auth, but still I have following concerns: Is this udid predicable and changeable that hacker is able to update to different one.