Based on previous work from PHP iCalendar i managed to build a slightly modified version of that tool to work on MySQL database with authentication and user management
You can download it through this Link
To load the files on the webSite i tipically use Sunbird , you should set the export path to:
http://[your host]/[your phpICalendar root]/calendars/publish.php/[your login name].ics
And then you will be asked for the username and password you defined on the userdb
This is distributed with NO WARRANTY and under the terms of the GNU GPL and PHP licenses. If you use it a notice or some credit would be nice.
You can get a copy of the GNU GPL at http://www.gnu.org/copyleft/gpl.html
You can get a copy of the PHP License at http://www.php.net/license.html