Yubikey type device issued by an authority trusted by the website owner. Same as we have it now with browsers and SSL certificates. We can even have a key issu

Yubikey type device issued by an authority trusted by the website owner. Same as we have it now with browsers and SSL certificates. We can even have a key issued by the government as a digital ID card. They can be used to check: is over 18, is real person, for digital signature, etc.