IIS x-forwarded-for help needed

Hello fellow HA friends, I have setup IIS with reverse proxy to my HA instance and all is working fine. However, everytime I log in it will say I am on a trusted network (ofc because the requests are coming from the proxy server which is on the internal network).

Now the thing to do according to the docs is to set up x_forwarded_for: true and set a trusted proxy. My proxy server lives on another server than my hassio install and so I pointed the trusted proxy to the correct server. All is working fine, however the headers don’t seem to work. I have enabled logging on the IIS server and I have even added a custom http header named X-Forwarded-For in IIS but it doesn’t seem to do anything. All requests are still shown as coming from the proxy server. Obviously this is a massive security risk if I’d leave the trusted networks config intact so I have disabled this for now. If I do a direct portforward with an ssl certificate this problem does not exist (but obviously I want to use reverse proxy hence this thread).

Is there anyone with IIS knowledge that could assist me with this? Your help is very much appreciated. (note that before asking this question I did search through the forums and tried to find answers elsewhere but after hours of searching I gave up for now and ask you guys here)

Thanks in advance!