HTTPS
HTTPS cannot work without a "certificate" file. That's why, when you activate HTTPS in the Admin-panel, you get something like this:
The easy way is to let HFS automatically make a basic certificate (clicking the "make one" link). But this easy solution has the downside of showing an ugly warning to the final user
screen.mp4
You can get a better certificate, one that shows no warning, and feed it to HFS. There are several companies selling certificates, but you can get one for free at https://letsencrypt.org/ .
A certificate file comes with another file called "private key". It's very important to keep these files private, so never have them in your "shared files".