How to setup website authentication
WebSumo - Setup Website Authentication
To setup website authentication, we must be on Builder page. Select any page you would like to add an authentication. Click 
on Property. Click 
on third menu after clicking an arrow. You will see Authentication. If you haven't set up an authentication, click Setup Authentication link.
After clicking Setup Authentication, this will set an authentication and you can select Needs Login or Login Page.
What these Options do :
Needs Login : The page will need to log in first before can be accessed
Login Page : This will be a main login page (Any pages which Needs Login option is on, will automatically redirected to Login Page if not login yet)
When clicking Login Page, there is an option to turn on Can sign-up. If Can sign-up option is turned on, you can register from Login Page. Please note that Can sign-up option is only available after clicking Login Page.
For reference, see youtube video below.