When we access one website, the site usually should have a mechanism to keep track of the status of the user on the site. There are a few mechanisms supported by many server side languages to help track user status such as session and cookie.Today we will talk about session, when creating a session, we need to keep track of many data, besides user data, we also need to tell the server what is the timeout of the session so that we can garbage collect the session data which should not be stored anymore. How do we implement a reliable session mechanism?In PHP, we are often told that we can change...