Once you have an Access Group set up, you can set a Sitewide Restriction. This restriction protects your entire site and will prompt all visitors to log in.
When logged into your WordPress Dashboard, navigate to Access and then To Entire Site.
To enable the feature, select the checkbox to the left of Restrict the entire site to this group and select the appropriate Access Group from the drop-down menu.
Once you’ve selected the correct group, click the Save button.