GetCertificate.
        [Preview API]
        :param str publisher_name:
        :param str extension_name:
        :param str version:
        :rtype: object

def get_certificate(self, publisher_name, extension_name, version=None, **kwargs):
        """GetCertificate.
        [Preview API]
        :param str publisher_name:
        :param str extension_name:
        :param str version:
        :rtype: object
        """
        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)