what does VPN has to do with it? And its actually a very bad solution here (if it even is a solution at all)
You obviously didn't understand what was said.
If the connection you are trying to secure is within your local LAN, then you don't need a publicly trusted certificate. [both, source and destination, are in same LAN]
You can use any other method to secure that connection - including using a private VPN.
I already said that Im using LAN only for simplicity. Obviously HTTPS is not the only concern there as I also said it before.