code: def verify_request(self, query, binding):
          
          resp_args = {}
          if not query:
              logger.info("Missing QUERY")
              resp = Unauthorized("Unknown user")
              return resp_args, resp(self.environ, self.start_response)
  
          if not self.req_info:
              self.req_info = IDP.parse_authn_request(query, binding)
  
          logger.info("parsed OK")
          _authn_req = self.req_info.message
          logger.debug("%s", _authn_req)
  
          try:
              self.binding_out, self.destination = IDP.pick_binding(
                  "assertion_consumer_service",
                  bindings=self.response_bindings,
                  entity_id=_authn_req.issuer.text,
                  request=_authn_req,
              )
          except Exception as err:
              logger.error("Couldn't find receiver endpoint: %s", err)
              raise
  
          logger.debug("Binding: %s, destination: %s", self.binding_out, self.destination)
  
          resp_args = {}
          try:
              resp_args = IDP.response_args(_authn_req)
              _resp = None
          except UnknownPrincipal as excp:
              _resp = IDP.create_error_response(_authn_req.id, self.destination, excp)
          except UnsupportedBinding as excp:
              _resp = IDP.create_error_response(_authn_req.id, self.destination, excp)
  
          return resp_args, _resp
docs: :param query: The SAML query, transport encoded
          :param binding: Which binding the query came in over