private function _get_jwt_aud_uri($method)
    {
        $last_slash_idx = strrpos($method, '/');
        if ($last_slash_idx === false) {
            throw new \InvalidArgumentException(
                'service name must have a slash'
            );
        }
        $service_name = substr($method, 0, $last_slash_idx);

        if ($this->hostname_override) {
            $hostname = $this->hostname_override;
        } else {
            $hostname = $this->hostname;
        }

        return 'https://'.$hostname.$service_name;
    }