Reverse Proxy with Oracle APEX

Need help setting HAProxy as a Reverse Proxy for my Oracle APEX applications.

Currently, my apps are accessed through their respective URLs like the ones here:
apexapp1.mydomain.com/ords/f?p=100
apexpp2.mydomain.com/ords/f?p=200
and so on…

Also, I have created an internal DNS that points to the machine that hosts HAProxy (myInternalDNSApp1.mydomain.com) and I would like that when the user goes to this url HAProxy will redirect him/her to the apexapp1.mydomain.com/ords/f?p=100.

Here is my haproxy.cfg file:
global
log 127.0.0.1 local2 debug

chroot      /var/lib/haproxy
pidfile     /var/run/haproxy.pid
maxconn     4000
user        haproxy
group       haproxy
daemon

# turn on stats unix socket
stats socket /var/lib/haproxy/stats

defaults
mode http
log global
option httplog
option dontlognull
option http-server-close
option forwardfor except 127.0.0.0/8
option redispatch
retries 3
timeout http-request 10s
timeout queue 1m
timeout connect 10s
timeout client 1m
timeout server 1m
timeout http-keep-alive 10s
timeout check 10s
maxconn 3000

frontend http_in
bind *:80
mode http
option httplog

acl host_launchpad hdr(host) -i myInternalDNSApp1.mydomain.com

use_backend launchpad if host_launchpad

backend launchpad
balance roundrobin
option httplog
server app1 apexapp1.mydomain.com/ords/f?p=100 check

So far, when going to myInternalDNSApp1.mydomain.com it always takes me to the apexapp1.mydomain.com/ords/f?p=4550 site (which is the admin page). I believe HAProxy is stripping out the f?p=100 part of the url which leaves myInternalDNSApp1.mydomain.com/ords and by default this always takes you to the admin page.

any idea on how to force and keep the f?p=100 part of the url?

thanks.

Basically

I was able to figure it out after upgrading haproxy to its latest version and using

http-request set header /mypath