Actually I don't think I am for DRM.
It's just for a check if user is a real user who has itch.io account. If he is a real itch.io user, than get his user name and ask itch.io if user with that name had legally bought the game. The game will start only if itch.io responses okay. Is that DRM bro lol
AAA games are not always hackable. I found COD MW 2020 isn't hackable. It has a strong checker that checks if player really bought their games legally.
I am not so strong with two arms only. But I leave this to itch.io api to check player ownership. Or maybe as previous response said about OAuth to use, which maybe better I guess. I'll research more ways out.
Let me see if I OAuth is better...