I think you're misunderstanding the GP. The HTTPS connection will not be redirected when you are behind a captive portal, you'll receive an invalid certificate

I think you're misunderstanding the GP. The HTTPS connection will not be redirected when you are behind a captive portal, you'll receive an invalid certificate error (when the captive portal tries to serve itself at that address) or the website will simply not respond. Only if the HTTPS response is cached in your browser would the redirection work behind a captive portal.