HAproxy - authentication popup

Hi
This is my first forum post. Hi everyone. And thank you all in advance.
Help and advice (in addition to the documentation :-)) are always useful.
I have HAProxy version 1.7.5-2 in production with hundreds of services, frontend and backend exposed and balanced without any problem.
Now I need to balance a website (443) that requires authentication with a popup form to log in.
It’s a third party product so I can’t change this.
When calling the url directly a popup appears.
If I expose this url through the HAproxy no popup is displayed. I have not yet understood where the problem is … I am proceeding by exclusion … but is there the possibility through HAproxy to pass authentication credentials directly to a form?
Thanks

Mich

Sure, haproxy is not supposed to interfere.

If you are suspecting haproxy, elaborate. Share configuration, output of haproxy -vv, explain what the headers are supposed to look like and how the actually look like, etc.

Hi, thx for reply. I found that popup was NTLM authentication.
Using the option http-keep-alive (both frontend and backend) solved my problem.

Thanks
Mich