by Manuel Razzari on WordPress.org

Settings screen. This is all there is to it.
Users who are not logged-in will be 302 redirected to an absolute URL specified by the admin.
Any user who can log in, from admins to subscribers, will be able to access the site.
To turn off this redirection, clear the redirect URL field, or simply disable this plugin.
This is a very minimal plugin for very simple use cases, when you want to avoid the bloat of a full-on redirection plugin.