A BEGINNER'S GUIDE: CROSS-DEVICE PASSKEYS

Summary from the TLDR InfoSec newsletter

A common challenge to passkey adoption is a user's difficulty signing in on a device that doesn't have the passkey installed and can't retrieve it from a cloud password manager. Hybrid transport addresses this issue by enabling cross-device passkeys, allowing a user to use another device's passkey to sign in. The flow involves the site the user wants to authenticate to generating a QR code, which the user then scans with another device. That second device performs a challenge-response with the server and a proximity check using BLE with the first device. If the challenge succeeds, the user is logged in on their original device.