Cross-device sign-in
Sitting at a desktop with no passkey registered on it, but a passkey on your phone? The browser's account picker offers "use a different device" — pick it, scan a QR code, and your phone completes the ceremony over Bluetooth proximity (this is the hybrid transport, sometimes called caBLE). The desktop never touches your phone's private key; it relays an encrypted tunnel the phone and the relying party's browser session negotiate directly.
There is no separate code path for this
This is deliberately the shortest page on the site. The demo below is the
exact same navigator.credentials.get() call as the
Authentication page — nothing here is
cross-device-specific. The browser and operating system handle hybrid
transport entirely on their own; the server's job (and this page's demo code)
doesn't change one bit whether the assertion came from a fingerprint sensor
three inches away or a phone across the room.
To actually see the cross-device flow, you'd need a second device: open this site on a phone, register a passkey there, then come back to a desktop browser and choose "use a different device" when this demo prompts you. Automated testing can't drive that QR/Bluetooth handshake — a virtual authenticator can't stand in for an actual second device — so unlike every other demo on this site, this one is verified manually rather than by an end-to-end test.