If you’re on iOS, you can lock it behind faceID. It’s an iOS feature so you don’t have to wait for developers to add it.

Also, it’s probably assumed that if you have the password or biometrics to gain access to the device, then you should also have access to the apps. At least that’s how Android handles it, iOS is a lot more strict when it comes to that. You can’t do anything of consequence on an iPhone without first passing biometrics.