Turn off authentication

Do you mean Two-factor authentication for Apple ID?

This cannot be turned off. See the linked document.

However, if you have recently activated it you have a small period of time in which you can turn it off:

If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll within two weeks of enrollment.