Duo has support for U2F, see https://guide.duo.com/u2f this would be an added bonus for incorporating Duo support in kolab_2fa. If this is out of the scope of kolab_2fa I would understand.

I have a working plugin with Duo but I don't know enough to integrate it with kolab_2fa. The code is here: https://github.com/leonardomarino/duo_auth can someone point me in the right direction?