code: def gen_def_json_scheme(self, req, method_fields=None):
          
          json_dict = dict(
              ApplicationId=req,
              RequestId=req,
              SessionId=req,
              Password=self.auth.password,
              Username=self.auth.username
          )
          if method_fields is not None:
              json_dict.update(method_fields)
          self.logger.debug(json.dumps(json_dict))
          return json.dumps(json_dict)
docs: Generate the scheme for the json request.
          :param req: String representing the name of the method to call
          :param method_fields: A dictionary containing the method-specified fields
          :rtype : json object representing the method call