Checklist

Obtain a FQDN for each “Protected Domain” and authelia.<domain.com>
Add authelia.<domain.com> to your DNS records
Obtain SSL certificates for authelia.<domain.com> and for Protected Domains
Configure Router to Open Ports 80/443 and forward to packets to server running reverse proxy
Configure server running reverse proxy to forward packets
Adjust firewall settings on router and server running reverse proxy to allow for incoming traffic.