The web application I am load testing is written in Java.  Apache is the web 
server, WebLogic the web container.  We are using SiteMinder for user 
authentication.  First I will describe the scenario:

1.  Send HTTP Request to login user. Siteminder logs user in successfully and 
sends a FORMCRED cookie back to the client.  
2.  The second HTTP Request to any page on the site works successfully.  It 
sends back the FORMCRED cookie to the server.  SiteMinder picks up the 
FORMCRED cookie, validates it and sets it to null (or empty string) and sends 
back a SMSESSION cookie.  
3.  The third and all subsequent requests then send SMSESSION cookie
to the server.  They dont send the FORMCRED cookie anymore since it is now 
null. 

This is how IE and Netscape work when sending cookies to the server.  Neither 
of them send cookies with null value back to the server.  JMeter, on the other 
hand, sends all cookies back to the server even if they have been nulled out.  
So, on the third request JMeter sends FORMCRED back to the server.  SiteMinder 
sees it and tries to validate it.  Since FORMCRED is null (or empty string), 
SiteMinder kicks the user back to the login page.  Thus my test case fails 
when I run it in JMeter.  

I fixed this issue my modifying 
org.apache.jmeter.protocol.http.control.CookieManager.java file.  I modified 
the public void add(Cookie) method.  Below is my modification:

/**
    * Add a cookie.
    */
   public void add(Cookie c) {

      /** My Modification Start */
      if (c.getValue() == null || c.getValue().equals("")) {
         removeCookieNamed(c.getName());
      }
      /** My Modification End */
      else {
         JMeterContext context = getThreadContext();
         getCookies().addItem(c);
         if (context.isSamplingStarted()) {
            context.getVariables().put(c.getName(), c.getValue());
         }
      }
   }

I am not sure if I have fixed a bug or if the bug is in SiteMinder since it 
should be reading FORMCRED if it is null.  Either way, I wanted to submit my 
modification and let you decide if you want to put it into JMeter.

Nizar Noorani
Consultant, Tallan, Inc.
noorani_786@yahoo.com