This is called an SSL Wildcard and is more expensive than a Dedicated SSL but it authorized for your domain and all sub-domains.
If you would like to order a SSL Wildcard you would simply change the common name to *.domain.com as per below:
Common Name: *.webafrica.co.za
Please visit https://www.webafrica.co.za/ssl-certificates/ for a full list of our SSL certificates. You can order these from the same page