It would be really helpful to have the option to automatically let guests login to a guest user via an QR code. It could be similar to the QR codes we are used to share our wifi.
Scanning the code could open the home assistant ip and prefill the authentication data.
There is an addon out there that introduces that kind of does the trick: The Completely Frictionless Way to Let Guests Use Home Assistant - Nathan Orick
But as the author states: it is not very safe.
If the data would be only stored in the QR code data, it would be only accessible by seeing the QR code, so the security risk is really low in comparison.