Should I allow emojis in my usernames?

Question

I'm implementing a new user authentication system for my mobile app and was constructing my username rules, i.e. less than 40 characters, alpha-numeric, etc.. when I thought about why I should only limit it to alpha numeric.

I don't have any issues from the application view - they can use emojis and foreign characters for all I care. I've been trying to figure out reasons why I shouldn't allow it but couldn't think of any good reasons other than it might be non-intuitive for users to search by username if it's just an emoji. Are there any other reasons or landmines that I'm overlooking? I'm using GraphCool as my backend-as-a-service.

Answer 1

If it makes it difficult to login in any way - like the user can't access the emoji from certain keyboard then no.

Answer 2

Theoretically there is no problem with that. Theoretically unicode works. In practice it managed to crash a lot of ios devices.

That's also good to know: https://security.stackexchange.com/questions/95847/advantages-to-alphanumeric-only-usernames

I would not recommend allowing just any character as a username. You could allow a few selected characters, but allowing any character is probably a security risk.