Synchronisation of external user database

Hi!

I'm setting up a Moodle 2.6.5 environment that syncs it's user base with an external MySQLdatabase for authentication. So far, I've managed to connect the database in the plugin and Test Settings does not produce any errors. 

Now, I'm trying to find out how to get the synchronisation going. The cron.php execution does not feature a line on importing or synchronising with the database. Do I have to modify the cron.php file to get this working or am I missing steps to take?

Help for this issue is kindly appreciated!

Thanks!