Can't get SSL Client Certificate

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Hy,
I've got problems getting ssl client certificate.
I'm using tomcat 4.1.2, Apache 2.0.42, mod_jk2 (2.0.0) and I've configured
Apache with SSL client verification and mod_jk2 with normal socket 
connector to port 8009.
All seems to work fine: 
the browser ask me the pin for the access to the key and then I can access
my servlet in tomcat, but I always get null when I try to access 
information about the client certificate.

This is the servlet code that I use to access the request attributes:

    java.util.Enumeration attributeNames = request.getAttributeNames();
    while(attributeNames.hasMoreElements()) {
      out.println("<p>Attributo</p>");
      out.println("<p>" + attributeNames.nextElement().toString() + 
"</p>"); 
    }
    out.println(request.getAttribute("javax.net.ssl.peer_certificates"));
 
out.println(request.getAttribute("javax.servlet.request.X509Certificate"));

What I'm doing wrong???
TIA
Mauro