Add android secure password storage

lib/src/settings/settings_service.dart

@@ -1,3 +1,5 @@
+import 'dart:io';
+
 import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
@@ -9,6 +11,17 @@ import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 /// you'd like to store settings on a web server, use the http package.
 class SettingsService {
 
+  FlutterSecureStorage getSecureStorage() {
+    if (Platform.isAndroid) {
+      AndroidOptions getAndroidOptions() => const AndroidOptions(
+            encryptedSharedPreferences: true,
+          );
+      return FlutterSecureStorage(aOptions: getAndroidOptions());
+    } else {
+      return const FlutterSecureStorage();
+    }
+  }
+
   /// Loads the User's preferred ThemeMode from local or remote storage.
   Future<ThemeMode> themeMode() async {
     final SharedPreferences prefs = await SharedPreferences.getInstance();