Redirecting http to https without mod_rewrite - apache

Question

I'm using an app (MediaCP) that thinks both HTTP and HTTPS can coexist on the same port. I cannot modify the code since it uses IonCube and some other­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­ shenanigans, but I could edit the JS player, or add files if needed. Since it's minified it's hard to know where to look for, I'm attaching it if you want to take a look at it: https://pastebin.com/DiCnMq32
The thing is that when I request a .js file while being on an HTTP page, it tries to load the content using HTTP, probably because it uses /// as a request protocol...
If entering https://mywebsite.com, then the jwplayer.js file loads https://example.com:2000/jwplayer.flash.swf and works just fine
If entering http://mywebsite.com, then the jwplayer.js file tries to load http://example.com:2000/jwplayer.flash.swf and it fails with a 400 error since the server obviously expected an HTTPS handshake. It doesn't matter that jwplayer.js was loaded using https.
I've been using ErrorDocument 400 to redirect these requests to HTTPS but the REQUEST_URI is lost on the process...
ErrorDocument 400 https://example.com:2000
This work just fine for users trying to login, but when entering http://example.com:2000/jwplayer.flash.swf it will always redirect to https://example.com:2000 and the JS code won't work.
I cannot use the REDIRECT_ server variables, because of the https:// prefix, that makes Apache think that the redirect is going to a remote server and by default it won't sent those headers.
I cannot remove the https://example.com:2000 prefix to use a local php / cgi file since it causes an infinite loop (oh, https is wrong lets try to load the 400 error page, oh https is wrong, lets...). Perhaps using a ScriptAlias would override the HTTPS check? I haven't got any luck with it but I'll try if you think it will make it work.
I've also tried to add %{REQUEST_URI} to the ErrorDocument line but it seems the variable is always empty.
Any ideas?
PS: I´m using Apache 2.4.25 on CentOS 7

Answer 1

Try to reference the JavaScript files as src="//url/somfolder/somefile.js" in the tags, it should use the current ref prefix http: or https: without specifically calling it out. Example:
<script src="//example.com/script.js"></script>
Note CSS can be referenced in a similar fashion:
<link rel="stylesheet" href="//example.com/style.css">