How could I found that user was redirected from other domain?

I have a frontend configured to check for specific domain in http request and then redirects that user to other domain. Each user redirected that way should be then forwarded to certain backend on the same Haproxy. How could I found that the user was redirected?
‘http-request redirect … set-cookie’ directive doesn’t work for me since cookie belongs to other domain and redirected browser will not send it in request. I cannot set the domain attribute to cookie since it doesn’t supported by ‘http-request redirect’ directive.
I also cannot get referer header from redirected browser request since most browsers use strict-origin-when-cross-origin referrer policy.
What are other options?