According to the docs, it seems that the relay only need to allow the transport, then it would work like any FIDO2 key: "hybrid" missing here: https://github.com/webauthn-open-source/fido2-lib/blob/9da9eb90f32f8f6bc49eabd2d9873872812c6323/lib/validator.js#L145 Docs: https://passkeys.dev/docs/reference/terms/#cross-device-authentication-cda