The issue I'm seeing is that I'm not able to get the proxy to set a cookie, any cookie, but JSESSIONID in particular. The test I've run is with a target application that does basic authentication.
The client sends the credentials correctly and the users is logged in correctly, and I can see the following header from the backend:
JSESSIONID=v6OmD_TlluOcpSFr0GcpkqnR.dhcp-208-183; path=/backend-system-path
Since client only knows about the proxy, this will not be set by the browser. Instead we want something like ProxyPassReverseCookiePath, ProxyPassReverseDomain like mod_proxy.