You can enable domain level or directory level authentication for your website. This will prompt visitors to enter a username and password before they can proceed further.

The benefits of this level of authentication is typically for websites / apps that are in development and where you want only authorized users to be able to view.

To enable, go to the server that houses the sites you want to add authentication for > select the site > select Site/Path Restriction > and then select Add Path. Then, fill in the path to add the lock to and add user credentials (username and password) that can access the site.