HAProxy: Rewriting help needed (hiding folder)

[CommWest]

Hi there!

I'm having huge problems understanding the rewriting options in HAProxy with pfSense.
What i want to accomplish is quite simple theoretically (in my opinion...).

User calls "sub.domain.com" and gets content from "sub.domain.com/folder/index.html" (but only "sub.domain.com" is shown as address by browser).
I know, that this is often done on the webserver itself, but this not possible here.

Can anyone help me with the backend-config, please?

Thank you!