Sounds like a crappy implementation of the authentication server then, and the sysadmin deserves a paddlin’ for not stripping non-UTF characters (or making sure they work).
My problem with using emojis as part of the password would rather be that while I might be able to enter them on my personal Android phone using the exact keyboard app I have installed right now, I might find myself struggling on a desktop computer or any other phone that doesn’t have this exact keyboard installed. After all, the graphical representation of the same emoji might look different there, and there is a chance I couldn’t even recognize it.
So if anything, I’d say use a non-UTF keyboard like Thai or Chinese, but then a standard character in that specific type. Keyboards layout can be installed across devices and are fully standardized, even if the same character looks slightly different.
Stripping characters from passwords, great idea! Right up there with truncating passwords that are too long.
Learn how to sanitise your database inputs first, damnit!
Doing that is actually a great way to tell attackers that you’re vulnerable to that type of attack.
Bypassing those front end restrictions is super easy, and the attackers don’t need an account or a password to attack you.
It’s like putting a sign that says “lock fragile; don’t tug” on the door to your business.
That’s not how any of this works.
First of all, stripping passwords is never okay. You can reject the password and let the user choose a new one, but never just modify it on your own.
Then, if your system is at risk of code injection by certain characters in user input, please just shut it down and never turn it on again.
