Challenges to add custom error page

Hi,

I have W2012 R2 and Exchange 2013 there. Idea is to add a custom error page for the 403.4 error, so that users are redirected to the correct URL if they by some reason end up to OWA without HTTPS.

I know the instructions to setup the redirect on the main page, but I try to make a bit more professional solution :D

So I have added on the OWA's web.config a lines:

        <remove statusCode="403" subStatusCode="4" />
        <error statusCode="403" subStatusCode="4" path="https://email.internalsite.com/owa" responseMode="Redirect" /> 

But that only gives me an empty page. What could be the reason that the redirect does not work?