juliansteenbakker/flutter_secure_storage ? reverse-engineered prompt

Build me a Flutter package that lets an app save sensitive things like tokens, passwords, and user settings in a secure key value store.

It should work on Android, iPhone, Mac, Windows, Linux, and web, and use the right secure storage method for each platform. On mobile, I want encrypted storage and the option to require biometrics or device authentication before reading data. On iOS and macOS, let me choose when stored values are accessible, like after first unlock. On Android, make the secure storage the default and include a simple way to migrate old saved data safely if the encryption setup changes.

I need the basic stuff to be easy to use, like write, read, delete, delete all, and check if a key exists. Please keep the API simple for app developers, with a default setup that works out of the box, but allow platform specific options when needed. Also make sure it behaves correctly on web only in secure environments like HTTPS or localhost.