This repository contains a simple example that implements FIDO/U2F keys in SSH using the Go language.
The example shows how to use an ed25519-sk key from the client side without changing the original SSH library code. To
use ecdsa-sk keys, you can make similar small tweaks.
The needed changes are minimal, and the key challenge is not to modify the existing SSH library.
I have successfully tested this on my YubiKey.