[tulir]

I'm pretty sure the server also needs to support it. The U2F signature stuff is different from SSH, so it needs a new authentication protocol: https://github.com/openssh/openssh-portable/blob/master/PROT...

[microtonal]

You are right. There is also more information here:

https://marc.info/?l=openssh-unix-dev&m=157259802529972&w=2

This step is very straightforward; append the public key to authorized_keys as you would normally. Note that U2F keys are a new OpenSSH key type, so the server must support it too.

I guess it will take a few years until all servers are upgraded.