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, just by clicking the "make one" link. But this easy solution has the downside of showing an ugly warning to the final user. This is what the user will see:
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".