HAproxy: port range

[alexschomb]

I was asked to establish a port porwarding for a specific TLD to an external address. The forwarding should succeed for certain ports in a port range. All other ports should be handled by OPNsense / the network behind.

As all requests will be HTTP/HTTPS only I thought that HAproxy would be a nice solution. But then I figured out that port ranges or empty values won't be accepted by the OPNsense plugin. Is there any solution how I could implement this anyway? HAproxy itself seems to support portforwardings (frontend) and empty port values (server), look at this question & answer:
https://stackoverflow.com/questions/26794547/how-to-configure-haproxy-port-range-to-range-one-by-one#33436983