code: def get_certificate(self, publisher_name, extension_name, version=None, **kwargs):
          
          route_values = {}
          if publisher_name is not None:
              route_values['publisherName'] = self._serialize.url('publisher_name', publisher_name, 'str')
          if extension_name is not None:
              route_values['extensionName'] = self._serialize.url('extension_name', extension_name, 'str')
          if version is not None:
              route_values['version'] = self._serialize.url('version', version, 'str')
          response = self._send(http_method='GET',
                                location_id='e905ad6a-3f1f-4d08-9f6d-7d357ff8b7d0',
                                version='5.0-preview.1',
                                route_values=route_values,
                                accept_media_type='application/octet-stream')
          if "callback" in kwargs:
              callback = kwargs["callback"]
          else:
              callback = None
          return self._client.stream_download(response, callback=callback)
docs: GetCertificate.
          [Preview API]
          :param str publisher_name:
          :param str extension_name:
          :param str version:
          :rtype: object