how to read and write the FlutterSecureStorage in public package in flutter

Because many of my apps would use FlutterSecureStorage, so I define the FlutterSecureStorage in a public lib like this:

bool isLoggedIn = false;
String baseUrl = "";
String shareUrl = "";
String staticResourceUrl = "";
final pageStorageBucket = PageStorageBucket();
final storage = new FlutterSecureStorage();

enum ConfigType { DEV, PRO }

class GlobalConfig {}

I could expose the GlobalConfig in main.dart like this in public lib:

export 'src/config/global_config.dart';

but I just wanna to know how to use the storage after import the public lib in my app, I am using the public lib in my app like this:

      ref: main

how to read and write global FlutterSecureStorage when add dependencies of wheel lib? is it possible? or define the FlutterSecureStorage in each app is the best practice?