MitID is hard-required to sign into anything government or personal information required. Previously people would be handed a key-card (a white, fold-out card with a bunch of numbers on it. The numbers were one-time use, so the card would eventually run out, requiring a replacement after a few months).

These key-cards have been completely phased out. Now there is the MitID app or a key-device that is almost impossible to get (you'll basically have to prove that you don't have/can't use a smart phone).

The MitID app has almost no features at all. It's specifically used for authentication. You log into the gooberment website or bank website, then a encrypted, constantly changing QR code pops up. You open the MitID app on your phone, scan the QR code, and then you gain access.

This is all run through the private security company the Danish government has hired, called "NETS".