HTTPS is “secure HTTP”. Though using HTTPS isn’t a must for forums, but recommended. Forum members when they try to log in using a password if the site isn’t over an HTTPS, the browser throws a warning to the user.
Do you want to move a XenForo forum from a subdomain (like say forum.yourdomain.com) to the root domain (yourdomain.com)? The process is fairly simple and easy to follow. Here is a complete step by step guide.
A step by step guide to switching an existing XenForo installation from HTTP to HTTPS aka from http://domainname to https://domainname
A complete step by step guide to properly move a XenForo forum from an olddomain.com to newdomain.com without having any significant impact of SEO.
XenForo admin area isn’t inside a directory but is accessible via the admin.php file. So one can’t add htaccess based password protection to a directory