Client Certificate Information not available to Servlet running on Apache + WebLogic Configuration

I am trying to access the client certificate information from a JSP using the following code with no success:

import java.security.cert.X509Certificate;
X509Certificate certChain[] = (X509Certificate[]) request.getAttribute("javax.net.ssl.peer_certificates");

if( certChain != null )
{
     for (int i=0; i < certChain.length; i++)
     {
          String a = certChain[i].toString();
          System.out.println(a);
                //...
     }
}

The certChain array comes back null.  Apache has been configured to require SSL communication and client certificate authentication.  I have tried with WebLogic requiring and not requiring client certificates with the same results.  

I also tried the following code but the return value came back null also:
   request.getUserPrincipal();