it’s not mastercard but your bank. there are plenty of banks which implement mastercards 3ds via app (eg N26).
Just reaffirms my suspicions that I need to shop around. I'm traveling and putting enough money on this card to start looking at ones that actually charge a fee and have decent "rewbates", I mean "rewards".
Less sarcastically, thanks for the heads up. I'd be greatful for any other hints of people that might not hate their credit card provider they want I do.