At least for launch, webauthn is only supported for HTTP(S) origins. That means that it cannot be used in, for example, the background page of extensions.

Since the webauthn relying party ID is a domain, we would have to decide how to map origins with a non-DNS-based authority component into the RP ID space before allowing this.

This bug exists to capture any feedback on this limitation is is linked from the Chromium source code.