We had a similar need a while back, and open sourced our solution: [alley-oop](https://github.com/futurice/alley-oop) is a Dynamic DNS server with an integrated Let's Encrypt proxy, enabling easy HTTPS and WSS for web servers on a local network (LAN).
It effectively automates the process that's described in the article. Once you have it set up (you need a few DNS entries and a tiny Go server running somewhere), using it is as simple as issuing an HTTP API call to your alley-oop server with the LAN IP you have, and the DynDNS domain you want associated with it, and getting a valid cert in return. You're then ready to spin up your HTTPS server with it, and start serving LAN traffic with a valid cert.
It effectively automates the process that's described in the article. Once you have it set up (you need a few DNS entries and a tiny Go server running somewhere), using it is as simple as issuing an HTTP API call to your alley-oop server with the LAN IP you have, and the DynDNS domain you want associated with it, and getting a valid cert in return. You're then ready to spin up your HTTPS server with it, and start serving LAN traffic with a valid cert.