IdP 3.4.6 with Unicon plugin for external CAS

[Leonard J Peirce]

We've been using the plugin for a while and I'm attempting to
test the latest Unicon plugin for authentication via an
external CAS server for a new install of IdP 3.4.6.

The few steps in CAS plugin's README.md are simple.  I copy
in the requisite files (no-conversation-state.jsp and both .jar
files), update idp.properties, and update web.xml with the
provided snippet:

     <!-- Servlet for receiving a callback from an external CAS Server 
and continues the IdP login flow -->
     <servlet>
         <servlet-name>ShibCas Auth Servlet</servlet-name>
 
<servlet-class>net.unicon.idp.externalauth.ShibcasAuthServlet</servlet-class>
         <load-on-startup>2</load-on-startup>
     </servlet>
     <servlet-mapping>
         <servlet-name>ShibCas Auth Servlet</servlet-name>
         <url-pattern>/Authn/External/*</url-pattern>
     </servlet-mapping>

When I redeploy the IdP refuses to start.  In jetty.log I get

    java.lang.IllegalStateException: Multiple servlets map to path: 
/Authn/External/*: ShibCas Auth Servlet,ShibcasAuthServlet

When I do not add the above snippet to web.xml things seem to
work fine.

Is anyone else seeing this?  Or am I missing something?

TIA....

--
Leonard J. Peirce
Western Michigan University