Hello.

What I could suggest here is adding Nginx as a reverse proxy for your Node.js application. You can take a look at this tutorial here on how to setup the Nginx proxy for your Node application:

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-node-js-application-for-production-on-ubuntu-16-04#set-up-nginx-as-a-reverse-proxy-server

That way you will be able to install a Let’s Encrypt SSL certificate for your Nginx service. Note that you would need a domain name in order to be able to issue the Let’s Encrypt certificate.

Hope that this helps!
Regards,
Bobby