[Atiscant]

(Same reply as to another comment in this thread)

In Denmark the official identification app does basically this. When you to officially verify yourself for e.g. the bank, government sites or whatever you type a “username” (identity string that officially should not be linkable to you but in practice often is). The site then displays a QR code that you scan with phone and then approve with a slider. It is not perfect but it is fairly easy for everybody.