Access webGUI behind corporate firewall

Hi folks,

I have a situation Image may be NSFW.
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I used to connect to my router on port 18880 via a DynamicDNS. The problem is that very recently my corporate firewall/proxy restricted access to all ports other than 80 and 443.

Of course I already use ports 80 and 443 for Apache running on my NAS.

I have already set a Virtual Host on Apache, but it only forwards to http://router:18880, which is not accessible from behind my corporate firewall/proxy ("504 error: remote server did not respond...

Access webGUI behind corporate firewall