The flutter_secure_storage plugin can be used to store data safely in a Flutter application. Sensitive data is securely kept via this plugin, which offers keychain- and keystore-based implementations on iOS and Android, respectively.

Implementation

To your pubspec.yaml file, add the dependency for flutter_secure_storage:

dependencies:
  flutter_secure_storage: ^5.0.2
Code language: CSS (css)

Run the command flutter pub get to fetch the dependency.

Import the flutter_secure_storage package in your Dart file:

import 'package:flutter_secure_storage/flutter_secure_storage.dart';
Code language: JavaScript (javascript)

Check for the latest version on the plugin’s page.

Configure Android Version

In [project]/android/app/build.gradle set minSdkVersion to >= 18.
android {
  ...
  defaultConfig {
    ...
    minSdkVersion 18
    ...
  }
}Code language: JavaScript (javascript)

Initialize an instance of FlutterSecureStorage:

final FlutterSecureStorage secureStorage = FlutterSecureStorage();
Code language: PHP (php)

Store a key-value pair securely:

await secureStorage.write(key: 'keyName', value: 'secretValue');
Code language: JavaScript (javascript)

Retrieve the value associated with a key:

String value = await secureStorage.read(key: 'keyName');
Code language: JavaScript (javascript)

Update the value associated with a key:

await secureStorage.write(key: 'keyName', value: 'newSecretValue');
Code language: JavaScript (javascript)

Delete a key-value pair:

await secureStorage.delete(key: 'keyName');
Code language: JavaScript (javascript)

Read All Data

To read all the values, we will use the readAll method.

await _localStorage.readAll();Code language: JavaScript (javascript)

Delete All Data

To delete all entries, we will use the delete all method.

await _localStorage.deleteAll();Code language: JavaScript (javascript)

Reference

Write, read, and delete all data from local storage

Secure-local-storage-in-flutter

Flutter – How to save data locally?
flutter-how-to-save-data-locally

how-to-save-to-web-local-storage-in-flutter-web
https://stackoverflow.com/questions/56417667/how-to-save-to-web-local-storage-in-flutter-web
Reading, Writing, and Deleting API data in local-storage-in-flutter-web
securing-local-storage-flutter