When generating a HTML5 export of a project, the main .html file will have the following code:
<script src="http://code.jquery.com/jquery-2.1.3.min.js"></script>
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<link href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css" rel="stylesheet">
This is problematic if the page is hosted on a CDN via a https:// URL, since this will generate a security error that states that loading Mixed Active Content is not allowed (details at Mixed content - Web security | MDN).
It would be nice to have UE4 exported directories just host these three files locally, so that they could be loaded relatively with
<script src="jquery-2.1.3.min.js"></script>
<script src="bootstrap.min.js"></script>
<link href="bootstrap.min.css" rel="stylesheet">
which would follow the same https:// or http:// protocols that the main page used. This would make hosted pages less resilient to outages from external jquery and bootstrap CDNs.
If this does not feel like a good solution, then another method would be to create a dynamic JS script that loads these files, which loads the scripts by reusing the JS global “location.protocol” field, which is either a string “https:” or a string “http:”, depending on which one was used to load the current URL.
This change would fix e.g. the issue reported here: Fixes to play HTML5 builds on Itch.io - Platform & Builds - Epic Developer Community Forums, and also make UE4 builds directly hostable via copying to dropbox, which uses https:// hosting.