We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
Agreed, in its current state I wouldn‘t teach someone less technically inclined to solely rely on passkeys saved by the default platform if you plan on using different devices, it just leads to trouble.
Using a password manager is still the solution. Pick one where your passkeys can be safed and most of the authors problems are solved.
The only thing that remains is how to log in if you are not on a device you own (and don’t have the password manager). The author mentions it: the QR code approach for cross device sign in. I don’t think it’s cumbersome, i think it’s actually a great and foolproof way to sign in. I have yet to find a website which implements it though.
The site doesn’t need to implement this; the browser handles that part.
I confirmed this works and logged into Github using Google Chrome on my work computer using a passkey stored in Bitwarden earlier today. I had to enable Bluetooth for Chrome, since I’d had it disabled, but then everything else was seamless.