Loads the frontend entity id dynamically.
        See super class satosa.frontends.saml2.SAMLFrontend#handle_backend_error
        :type exception: satosa.exception.SATOSAAuthenticationError
        :rtype: satosa.response.Response

def handle_backend_error(self, exception):
        """
        Loads the frontend entity id dynamically.
        See super class satosa.frontends.saml2.SAMLFrontend#handle_backend_error
        :type exception: satosa.exception.SATOSAAuthenticationError
        :rtype: satosa.response.Response
        """
        idp = self._load_idp_dynamic_entity_id(exception.state)
        return self._handle_backend_error(exception, idp)