We wrote a plugin for Nagios which will check the status of a Cpanel server license. The plugin uses the Cpanel license web server (http://verify.cpanel.net) to verify the license status of a server. If the plugin cannot verify the license, or if the license has expired, it generates a critical error.

The plugin was written in Python and has been tested extensively here.

Download version 1 of this plugin: check_cpanel.py