If you get an authentication page during enrollment of your device, this means you have enrolled a device using the Global QR Code, which is found under the Enrollment tab.
This QR Code is user authenticated and its validity is unlimited in time. This QR Code validity is unlimited in time. A device enrolled with the Global QR Code must be user authenticated. For that, you first need to register your list of users. Then, during the enrollment, your users will be prompted to enter their credentials.
Are you looking for a QR code which isn't user authenticated? Please refer to the QR code under Profile Management > Profile Name > Enrollment.