private static function _init()
 {
     if (!self::$initDone) {
         global $mysqlConfig;
         self::$mysqli = new mysqli($mysqlConfig['host'], $mysqlConfig['username'], $mysqlConfig['password'], $mysqlConfig['schema']);
         self::$mysqli->set_charset('utf8');
         self::$hasher = new PasswordHash(8, false);
         self::$initDone = false;
     }
 }