Except in the real world almost every gym I've used just gives you a keychain barcode with your account number and it works fine. You scan in and it checks whether you're current. Maybe shows your picture to a front door attendant on their computer. No complicated cryptography required.

A gym requiring an app would be a hard no from me. I don't know why anyone (especially technical) would put up with that.

> I don't know why anyone (especially technical) would put up with that.

Answer from someone that has to put up with that: other gyms are significantly harder to get to (distance) and it’s already hard enough to get motivated to go. My options are shitty app or no gym.

Not everything is technically perfect and sometimes your only option is to put up with the stupidity of other developers/product managers.