Calling external applications from Jahia portal

Hello,

I am exploring the different capabilities for calling external
applications from the Jahia portal.
I have to solve the case with one Jahia running on one server and
hosting apps on its applications server (tomcat or another), and a
user authenticated on that Jahia server.
Now, I want to call a webapps or a portlet hosted on another
applications server (tomcat or another) from a Jahia context: I have
identified the future WSRP to call Remote Portlet in next versions of
Jahia, but is it possible to call external portlets (written in java)
with security context coming from Jahia and without WSRP protocol or
we can only use apps which are deployed on the same applications
servers as Jahia ?

Thanks by advance,

Dominique Pellat