Smartcards / YubiKeys.
Never understood the logic for these to be centralised / online.
For this and related reasons, such as enforcing protocol upgrades, most smartcard systems end up permanently online.
https://www.mitid.dk/en-gb/get-started-with-mitid/how-to-use...
For this and related reasons, such as enforcing protocol upgrades, most smartcard systems end up permanently online.