anchor.diff:          credentials['googleDriveRootFolder'] = rootFolderDriveId;
           CartSystem.instance.googleDriveRootFolder = rootFolderDriveId;
           CartSystem.instance.credentials = credentials;
  -        return (new File(CartSystem.instance.oauth['web']['credentialsFilePath'])).writeAsString(decoder.convert(credentials));
  +        return PinUtility.writeJsonFile(CartSystem.instance.oauth['web']['credentialsFilePath'], credentials, withIndent: true);
         } else {
           // just pass the result to next step
           return new Future.value(_);
  
positive.code:   static handleOauth2Next(HttpContext ctx) {
      String email = '';
      HashMap credentials = {};
      final decoder = new JsonEncoder.withIndent('    ');
  
      bool isAuthed = (CartSystem.instance.credentials.length > 0);
  
  
negative.code: 
    static Future<File> _updateSessionToken(HttpContext ctx) {
      String token = PinUtility.uuid();
  
      var expires = new DateTime.now();
      expires = expires.add(new Duration(seconds: CartSystem.instance.setting['cookieLive']));
  