Hi Scott,
Thank you for your reply. Actually, I needed the header to be present in the request when the form gets submitted. (So I wanted to intercept the FSSO request before the form submit action). I tried, but I did not manage to do this via HTTP Transformations, so I wanted to ask whether the problem is on my end or it is simply not possible. After doing more tries, I was leaning more and more towards the second option and solved my original problem without using FSSO.
Thank you,
Gergő