Unifi Controller "400 Bad Request" behind HAProxy

[ecramond]

I'm hoping someone can assist me in resolving an error I'm seeing while trying to access my Unifi Controller (v5.12.72) via reverse proxy (HAProxy 0.60_4). When I try to access the Unifi controller, I get to the Login screen but when I log in the controller throws up a 400 Bad Request Error. I don't have any issues accessing the controller from my local network nor do I have any issues accessing other sites I have running through HAProxy. Config for Frontend and Backend for Unifi is the same as for other Sites I've got set up. Any assistance would be greatly appreciated.