Pass session data in a Play chain for get and post methods

I have a chain of Play applications connected by REST/WS. A leaf (authentication module) adds session data (an hash) to the response:

Redirect(routes.SuperProprietorController.welcome()).withSession(messagesRequest.session + (SessionMessagesController.sessionTokenKey -> tokenValue))

its done to a post of form credentials. How to transfer the session data backwards over the gateway (entrance module) and with the next click forward to the authentication module to proof the session data? Maybe there is a difference between get and post?