I have [bitnami/wordpress] deployed on my kubernetes cluster, with default apache configuration, except the line:
LimitRequestFieldSize 32768 so I can theoretically send 32kb data in the header.

For lower amounts, the apache sent back 200 if the header was under limit and 400 if it was over limit. But for 16k and above, I only got 408 back, with no error logs to show why. Is there some php limitation or wordpress limitation that could be in play?

My header is at least 20k and can’t really make it smaller, and no external proxy limitations are in effect.

The command I used is:
curl -vk -H "X-Header: $(cat file16k)" https://url-to-my-wordpress:8443/wp-login.php

and I expected: 200, but I got 408.