Be able to login with a Yubikey token or Yubikey U2F (touch to login) without having to use a timebased OTP.
M.D. Klapwijk commented
And while you are at it, implement FIDO2 as wel. Mark knows more:
J Brunner commented
Please add this functionality to your SSL VPN, you are one OpenVPN plugin away from it being a reality. You already have username/password auth enabled on it, one more line in the server config file and bingo, 2FA VPN connections.
James Robey commented
Yeah do it now! https://developers.yubico.com/
Mike love this idea!