Haproxy + IIS passthrough cookies

We have an application that uses .Net and have authentication (tokens) cookies pass to the user when it authenticates in order to track him (login - logout). I tried to pass those cookies on haproxy but with no success. Does anyone has a working example on how to redirect those cookies to the user. I have haproxy 1.5.14. I tried it with SSL passthrough (mode tcp) and also with (mode http) some http settings (tweaking) that i found scattered on the web. The cookies never pass on the IIS server. I am using the haproxy as a reverse proxy just to clarify.

Thank you!