Decoding Plesk passwords

First time question.

I have a customer panel that shows the Plesk 12.5 password. For now I put that in manually when I generate the password. But customers change their password, forget it and then everything fails. I use the Plesk API to receive the password, but this is encrypted.

$5$CngpmNFXTsfRswHH$nntnTlj0KLkhEidK.XVWgbyv9HcAE8YV/fog0C6aG17

I found out that the key is found in /etc/psa/private/secret_key.

I tried:

$res_non = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $hash, 'ecb');

$decrypted = $res_non;
$dec_s2 = strlen($decrypted);

$padding = ord($decrypted[$dec_s2-1]);
$decrypted = substr($decrypted, 0, -$padding);

But that doesn’t return my password correctly.

Any help is appreciated, Thanks!