I didn't find useful documentation on the link you showed, but I may have missed it. Here's a general article on Wikipedia, I hope it will give you some hints and directions.
This document describes how to add WiKID two-factor authentication to SquirelMail. Please note that it uses radius, which is a feature of the commercial Enterprise version (it is a licensed 3rd party add-on). If you want to use the open source Community Edition, you will need to integrate the WiKID PHP network client with the SquirelMail web interface. The PHP network client allows you to add two-factor authentication to any php app and it is LGPL. I think a WiKID/Squirelmail plugin would be great.
I wrote that tutorial a long time ago, but I suspect it is still fairly accurate. I see that the install tutorial I used is stil up too: Quickstart: Fedora Core
Also, since I wrote that we have added mutual https authentication (the token client will validate that the SSL cert of target site matches the cert expected) which prevents network-based man-in-the-middle attacks. All you have to do it add the ssl SquirrelMail URL in the domain page on the WiKID server.
Download the PHP network client from our website: Network Clients � WiKID Strong Authentication
It has information and code examples on how to add WiKID two-factor authentication to PHP applicatons.
There is no such plugin. You would have to write it.
Just so you know, WiKID is still RPM-based and you will have some troubles running it on Ubuntu. Porting help is welcome and our next major release will support multiple OSs.