cPanel + reverse proxy = invalid security token

The system almost works, but I get the error in various places when logging into webmail and performing certain actions on WHM: HTTP error 401 Invalid Security Token Lots of XSRF errors in the console: Blocked a frame with origin "https://webmail.example.com" from accessing a frame with origin "https://cpanel.example.com". Protocols, domains, and ports must match. Refused to display 'https://cpanel.example.com/cpsess12345678/3rdparty/squirrelmail/src/webmail.php?login=1&post_login=12345678' in a frame because it set 'X-Frame-Options' to 'SAMEORIGIN'.
Additionally, I get unstyled pages in WHM where it is attempting to pull styles and content from cPanel but fails to do so due to the aforementioned errors. So far tried:

• Old hack for disabling XSS (xsrftoken=false), doesn't work on new cpanel
• Disable cookie based IP validation
• Force update
• Strip xss related headers using nginx
• Delete cache directory
• Praying to Lord Krishna

Still doesn't work.