Ew, DRM… on itch.io? Is that even allowed?! I thought the whole point of itch.io is DRM free indie games… well, that’s one way to get people to just watch a playthrough on YouTube or Twitch instead for the low cost of nothing. :/
It's itch.io themselves who provides the code to determine the purchaser email and they even give me some suggestion when I said I want to implement a program to determine if player is the purchaser/ person who got it as a gift from itch.