I keep a list of passwords in a text file, with one password on each line. I use a short script (rotatefile.sh) on the RADIUS server to pick up the password from the top of the file and put it at the bottom:

#!/bin/sh

Take first line of wordfile

pw=head -n 1 /root/wordfile.txt
echo "$pw"

Delete first line in wordfile

sed -i 1d /root/wordfile.txt

Append wordfile with word taken from top

echo $pw >> /root/wordfile.txt

I then call this script from within another script which picks up the password from the file and uses it to update the entry for that login on the RADIUS server. Whether you use a flat-file or a SQL backend, either way it works:

t4=/root/rotatefile.sh

The t4 environment parameter can then be used to perform a 'sed' change on your users file or be parsed into your SQL database. As Derelict has suggested, you can post the username on the form itself if you need to.

Define each "user-name-on-that-day" in the pfSense's Local user manager. Each with a password for that unique user (for that day). Every month, fill up you 29/30/31 users with new passwords (POTD).