Practically you dont need to apply security for the communication between Web tier and the
EJB tier ! Because no one is going to acess the EJB Tier directly, The initial request will be handled by the web tier then it forwards it to the BD which then goes to the EJB/Application Tier.
Also one major need of the scecure system is that your web server which receives the initial request should be inside the fire wall.
Hope this helps