public static function getRandomString($length = 16, $alphabet = "abcdefghijklmnoprstuvwxyz0123456789")
{
$chars = $alphabet;
$str = '';
for ($i = 0; $i < $length; $i++) {
$rand_key = mt_rand(0, strlen($chars) - 1);
$str .= substr($chars, $rand_key, 1);
}
return str_shuffle($str);
}