If using a web server for exactly the same domain name as your RTC service, it is possible to use the certbot command for your web server to setup the certificate the first time.

If there is no HTTPS web server for the domain, it is possible to use the certbot certonly sub-command to request a certificate.

As the certbot utility is still quite new and evolving, it is recommend that you consult the certbot web site for the most up-to-date detailed instructions.

After running certbot, the certificate files will be present at locations such as /etc/letsencrypt/live/example.org/fullchain.pem and the private key files will be present at locations such as /etc/letsencrypt/live/example.org/privkey.pem