from one web application you can call the other
StringBuilder url = new StringBuilder();
url.append("build the necessary url to go to other application");
ExternalContext extContext = context.getExternalContext();
Also, have a look at
if you are using jboss 5 +
<!-- Uncomment to enable single sign-on across web apps deployed to this host.
<Valve className="org.apache.catalina.authenticator.SingleSignOn" debug="0"></Valve>
Hope this helps
You could packaged them into one foo.ear and deploy them. So much simpler.
BTW for Authentication and Security, are you using Appache Shiro? Highly recommended.