login method
Implementation
Future<String?> login(String appId, String appKey) async {
var configString = Storage().getString('config');
configString ??= defaultConfig;
final config = ConfigResponse.fromJson(jsonDecode(configString));
readConfig(config);
this.appId = appId;
this.appKey = appKey;
loginObj = Login(appId, appKey);
return await innerLogin();
}