Using Freeradius authorization to send data to a microcontroller

I'm a relatively new freeradius user so I am not really an expert with it. In our project, depending on a user's authentication/authorization by the server, we need to send an "unlock/lock" byte to a microcontroller (connected to /dev/ttyUSB0, by the way). So where do I start with the solution? Can I run a certain code/program automatically once the server authenticates a user? Are there any previous applications similar to this? Our installed version is 2.1.0+dfsg-0ubuntu2, running on Ubuntu 8.10. The backend database we used is MySql. Thanks in advance. Rex Dizon