code: def handle_authn_request(self, context):
          
          internal_req = self._handle_authn_request(context)
          if not isinstance(internal_req, InternalData):
              return internal_req
          return self.auth_req_callback_func(context, internal_req)
docs: Handle an authentication request and pass it on to the backend.
          :type context: satosa.context.Context
          :rtype: oic.utils.http_util.Response
  
          :param context: the current context
          :return: HTTP response to the client