This would be a cool feature to have. Either have a way to login by URL or QR code. Imagine guests being able to login to your home assistant with their phones by scanning a QR code on your displayed home assistant tablet, instead of having to manually type in a given login/password.
I just thought of this now, it would be super cool. Sadly, two years on, no apparent way to do that.
It should be possible, for homebidge (IOS) qr codes ar generated by HA, so some functionality is present 
A must have feature. Especially with obnoxiously long passwords, having to type that in for new users is just 1990.