I'm running Kolab16 on Jessie and tried to enable kolab_2fa, but that failed with:
[24-Jan-2017 22:22:40 Europe/Berlin] PHP Fatal error: Class 'Yubikey\Validate' not found in /usr/share/roundcubemail/plugins/kolab_2fa/lib/Kolab2FA/Driver/Yubikey.php on line 48

I copied php-endroid-qrcode_1.5.4-1_all.deb and php-enygma-yubikey_3.2.0-1_all.deb
from Winterfell and installed the packages. 2FA with my yubikey works after the
initial configuration.

I think we also need dependencies added to roundcubemail-plugins-kolab to get the
packages automatically installed.