https://github.com/danstiner/rust-u2f implements pure software u2f for WebAuthn. I think that it may be possible to do better. For example implement the storage of secrets on a phone. When a phone is paired to a computer and KDEConnect on phone is active and the browser requests authn from desktop part of KDEConnect using u2f, it forwards the request to phone. The phone does the job and forward the response to desktop. On phone part either a pure software form can be used, or, for example, a usb or nfc one. Or it may even make sense to just implement the following stack (each component can be usable on its own): 1. ssh over kdeconnect 2. usbip over ssh 3. soft-u2f over usbip 4. u2f over softu2f