PHP MD5 with appended salt

Hi all, I am trying to connect my freeradius server to a mysql database containing all users. I created a new view to represent the table structure needed by freeradius, but I a problem with validating the passwords. The passwords of my users are (from a PHP application) concatenated with a salt, which is the same for all passwords, and stored using the regular php md5 function: md5($userpass . ':' . $salt) How can I make freeradius to append this salt to the password as well and validate the password in the correct way? Is there a default way to do this? Or should I create a module to do this? Regards, René