:param request: OAuthlib request.
        :type request: oauthlib.common.Request

def validate_grant_type(self, request):
        """
        :param request: OAuthlib request.
        :type request: oauthlib.common.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)