title: How to do this?
body: <p>I logged into an online forum created by using PHP and was browsing some topics in the web site.<br/>
  Since the weather was hot, I got to have a bath and left my computer idle for a short while. <br/>When I came back to my computer, I pressed a "Add Post" icon.<br/>
  But When I  pressed to submit the new topic,the web site redirected me to the Log in page, <br/>I gussed my cookie might have been expired. And then after I logged into the web site again, <br/>my new post was created. I am wondering how they do this. <br/>What is the method and technique they used?</p>
  
  <p>Did they store my new post to a new cookie or session first when they found that my cookie was expired? </p>