public static function useProduction($client_id, $client_secret, $api_version = null)
    {
        if (self::$production !== null) {
            throw new RuntimeException('API mode has already been set.');
        }
        self::$production    = true;
        self::$client_id     = $client_id;
        self::$client_secret = $client_secret;
        self::$api_version   = $api_version;
    }