[ Thanks to Falko
Timme for this link. ]
“So, you got yourself a nice OpenVPN box. People need to login
with their certificates but… if their laptop is stolen anyone
could login. Sure, you could add password login but thats a bit
outdated. The solution for this is using a OTP (one time
password).“This technique is being used by a lot of large corporations
including banks. This tutorial shows you how to configure OpenVPN
to add additional security.“This assumes you already have OpenVPN configured and working
properly.”