One-time set basic auth for all virtualmin servers

I am trying to set basic auth on all virtual servers from global Apache configuration file

Following this SO answer

I put this code at the end of /etc/apache2/apache2.conf, but nothing happens after server restarts

<Location "/">
    AuthType Basic
    AuthName "Collaborator"
    AuthUserFile "/usr/local/share/apache_basic_auth/.htpasswd"

Maybe there is any Virtualmin-specific setting for than

Note that I am trying to set authentication for all existing servers, not for new only