Hi Sridhar,
You should be able to use the Tomcat JNDIRealm configuration
(
http://tomcat.apache.org/tomcat-6.0-doc/realm-howto.html#JNDIRealm)
to define the authentication Realm for the tomcat server in the
conf/server.xml file.
I believe that Rundeck's web.xml also currently requires that each
authenticated user belong to a role named "user". This is hardcoded
in the web.xml for the rundeck.war, but you can modify the web.xml if
you need to change the default role requirement (look for the
<security-role>).