If you're trying to host both HTTP and HTTPS (TLS) on the same Forum, if someone were to post a link to lets say XenForo. The client is browsing the site on a different domain, the URL should change to http(s)://DomainHere.tld
Hopefully this makes sense. XenForo already does this with Navigation. However, it really is required in Posts if you're planning on using Multiple Domains/Protocols to serve up your site.