code: def validate_grant_type(self, request):
          
          client_id = getattr(request, 'client_id', None)
          if not self.request_validator.validate_grant_type(client_id,
                                                            request.grant_type, request.client, request):
              log.debug('Unauthorized from %r (%r) access to grant type %s.',
                        request.client_id, request.client, request.grant_type)
              raise errors.UnauthorizedClientError(request=request)
docs: :param request: OAuthlib request.
          :type request: oauthlib.common.Request