How to enable a Let's Encrypt certificate for the ISPConfig admin console

You can use Let's Encrypt certificates for the ISPConfig admin console too.
In order to achieve this, you can use the following commands:

### as super user of course
DOMAIN="www.mydomain.com"
letsencrypt auth --text --agree-tos --authenticator webroot --server https://acme-v01.api.letsencrypt.org/directory --rsa-key-size 4096 --email postmaster@${DOMAIN} --domains ${DOMAIN} --webroot-path /usr/local/ispconfig/interface/acme
dt=`date '+%Y%m%d%H%M%S'` 
cd /usr/local/ispconfig/interface/ssl/ 
for ext in csr key.secure key crt
do
 if [ -f ispserver.$ext ]
 then 
   mv ispserver.$ext ispserver.$ext.old.$dt
 fi
done
ln -s /etc/letsencrypt/live/${DOMAIN}/privkey.pem ispserver.key
ln -s /etc/letsencrypt/live/${DOMAIN}/fullchain.pem ispserver.crt
service apache2 restart