How to use the keystonemiddleware.auth_token._cache.SecureTokenCache function in keystonemiddleware

cache_kwargs = dict(
            cache_time=int(self._conf.get('token_cache_time')),
            env_cache_name=self._conf.get('cache'),
            memcached_servers=self._conf.get('memcached_servers'),
            use_advanced_pool=self._conf.get('memcache_use_advanced_pool'),
            dead_retry=self._conf.get('memcache_pool_dead_retry'),
            maxsize=self._conf.get('memcache_pool_maxsize'),
            unused_timeout=self._conf.get('memcache_pool_unused_timeout'),
            conn_get_timeout=self._conf.get('memcache_pool_conn_get_timeout'),
            socket_timeout=self._conf.get('memcache_pool_socket_timeout'),
        )

        if security_strategy.lower() != 'none':
            secret_key = self._conf.get('memcache_secret_key')
            return _cache.SecureTokenCache(self.log,
                                           security_strategy,
                                           secret_key,
                                           **cache_kwargs)
        else:
            return _cache.TokenCache(self.log, **cache_kwargs)

cache_kwargs = dict(
            cache_time=int(self._conf_get('token_cache_time')),
            env_cache_name=self._conf_get('cache'),
            memcached_servers=self._conf_get('memcached_servers'),
            use_advanced_pool=self._conf_get('memcache_use_advanced_pool'),
            dead_retry=self._conf_get('memcache_pool_dead_retry'),
            maxsize=self._conf_get('memcache_pool_maxsize'),
            unused_timeout=self._conf_get('memcache_pool_unused_timeout'),
            conn_get_timeout=self._conf_get('memcache_pool_conn_get_timeout'),
            socket_timeout=self._conf_get('memcache_pool_socket_timeout'),
        )

        if security_strategy:
            secret_key = self._conf_get('memcache_secret_key')
            return _cache.SecureTokenCache(self.log,
                                           security_strategy,
                                           secret_key,
                                           **cache_kwargs)
        else:
            return _cache.TokenCache(self.log, **cache_kwargs)

def __init__(self, log, security_strategy, secret_key, **kwargs):
        super(SecureTokenCache, self).__init__(log, **kwargs)

        if not secret_key:
            msg = _('memcache_secret_key must be defined when a '
                    'memcache_security_strategy is defined')
            raise exc.ConfigurationError(msg)

        if isinstance(security_strategy, six.string_types):
            security_strategy = security_strategy.encode('utf-8')
        if isinstance(secret_key, six.string_types):
            secret_key = secret_key.encode('utf-8')

        self._security_strategy = security_strategy
        self._secret_key = secret_key