#primaryily used to generate cert for mqtt broker usage. (standalone mode!)
https://tecadmin.net/how-to-generate-lets-encrypt-ssl-using-certbot/



#to get cert file locally.
128  sudo cp -r /etc/letsencrypt ~/letsencrypt-copy
129  sudo chown -R ubuntu:ubuntu ~/letsencrypt-copy
130  sudo chown -R mpuser:mpuser ~/letsencrypt-copy