Custom voucher login

[vi]

Could you please point me to the files I should take a look at to be able to alter the voucher validation?
I already have a voucher system that I would like to use on the captive portal.

My pfsense knowledge is limited to user stuff but my php skills should make up for that.
Thanks. :)

[dhatz]

The primary file is /etc/inc/captiveportal.inc

pfsense creates and uses files under /var, e.g. /var/etc