Potato is an easy to use one-time-password client. It adheres to the mOTP standard as detailed at motp.sf.net. It works hand in hand with server-side Potato which is a web interface, and a plugin for Freeradius.
Pro-tip: Click the one-time-password to copy it to the clipboard.
It do what it should do, and it do it great! With this app the security id to pair your VPN is random and unique!