Extauth script not working [PHP]

I'm trying to use this script to allow users from my existing MySQL database to connect to the ejabberd server (version 16.08) on Ubuntu 14.04.4 (Vagrant).
I changed the ejabberd.yml configuration file to setup external authentification.
The script is located in /etc/ejabberd/auth.php.
I changed the log level to debug and I got this error message :
[critical] extauth script has exitted abruptly with reason 'normal'

If have any piece of information to help solve that problem that'd be awesome, or need more information, I'm available !