Are php sessions persistent by default?
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From the course: PHP: Managing Persistent Sessions “ - In this chapter, we'll take a detailed look at the security implications of sessions, starting with a very basic overview of How PHP Sessions Work. This will lay the foundation for devising a strategy to minimize the risks of persistent sessions that don't require users to log in each time they visit a site. Basic communication between a browser and a web server is stateless. What that means is the browser sends a request to the web server, and
the server responds by sending the requested web page and associated assets, such as images and style sheets. Apart from knowing where to send everything, the server has no interest in who you are. Each request and response is treated independently. This stateless communication makes it impossible to preserve detail such as the visitor's name, preferences, or contents of a shopping cart. Cookies are one way of preserving information across multiple requests. The browser sends the request to the
web server in the normal way. When the server responds, it sends a cookie for the browser to store. This is a series of name-value pairs to identify the user together with information that's to be preserved between requests. The next time the browser sends a request, all the information in the cookie is sent back to the server. Although cookies can be encrypted, there's a danger that the information can be intercepted. It's also inefficient to keep sending information back and forth. Sessions
overcome these problems using a combination of a cookie and server-side storage. The browser sends a request to the server. PHP responds by sending a unique token that identifies the current session. This is known as the session ID. In all subsequent requests, the browser sends the session ID to say, "Hey, it's me again." All other data related to the session is stored on the web server. Only the session ID gets passed back and forth. There are two ways of propagating the session ID. It can
either be stored as a cookie in the user's broswer or it can be passed through the URL as part of a query string. Embedding the session ID in a query string exposes it in plain view to potential attackers. It's such a major security risk, we won't look at how to do it in this course. Always use cookies to store the session ID. Initializing a Session is very easy. Just invoke session_start(); close to the beginning of a script where you want to use session data. It doesn't need to be the very
first line of the script, but it must come before any output is sent to the browser. You store data that you want to be available throughout your application as session variables by adding them to the SESSION superglobal array. This example creates a session variable called 'authenticated' and sets its value to true. If the value comes from user input, it's often a good idea to sanitize it before storing it as a session variable. In this example, 'name' comes from the POST array, so it's passed
to htmlentities() before being assigned to SESSION 'name' If you don't sanitize user input at this stage, you need to remember to do so each time you display a value stored in a session variable. SESSION is a superglobal array, so it's available in every page that invokes session_start() By default, the cookie that stores the session ID expires when the browser is closed, but the data associated with the session isn't automatically deleted at the same time. It often remains on the web server
where it's stored in plain text. For security, it's best to delete session data that's no longer needed. However, it's difficult to guarantee that users will log out before leaving your site so it's not always possible. But that doesn't mean the data remains on the web server indefinitely. PHP garbage collection runs periodically to remove session data files that are out of date. This has implications for creating persistent sessions. First of all, we need to make sure that a cookie identifying
the user remains active even after the browser has been closed. We need to make sure that session data isn't garbage collected until it's genuinely no longer needed. And we need to store the data as securely as possible. With these points in mind, we'll next examine the options for configuring PHP sessions. ContentsA session is a way to store information (in variables) to be used across multiple pages. Unlike a cookie, the information is not stored on the users computer. What is a PHP Session?When you work with an application, you open it, do some changes, and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are or what you do, because the HTTP address doesn't maintain state. Session variables solve this problem by storing user information to be used across multiple pages (e.g. username, favorite color, etc). By default, session variables last until the user closes the browser. So; Session variables hold information about one single user, and are available to all pages in one application. Tip: If you need a permanent storage, you may want to store the data in a database. Start a PHP SessionA session is started with the Session variables are set with the PHP global variable: $_SESSION. Now, let's create a new page called "demo_session1.php". In this page, we start a new PHP session and set some session variables: Example// Start the session // Set session variables Run example » Note: The Get PHP Session Variable ValuesNext, we create another page called "demo_session2.php". From this page, we will access the session information we set on the first page ("demo_session1.php"). Notice that session variables are not passed individually to each new page, instead they are retrieved from the session we open at the beginning of each page ( Also notice that all session variable values are stored in the global $_SESSION variable: Examplesession_start(); // Echo session variables that were set on previous page Run example » Another way to show all the session variable values for a user session is to run the following code: Examplesession_start(); print_r($_SESSION); Run example » How does it work? How does it know it's me? Most sessions set a user-key on the user's computer that looks something like this: 765487cf34ert8dede5a562e4f3a7e12. Then, when a session is opened on another page, it scans the computer for a user-key. If there is a match, it accesses that session, if not, it starts a new session. Modify a PHP Session VariableTo change a session variable, just overwrite it: Examplesession_start(); // to change a session variable, just overwrite it Run example » Destroy a PHP SessionTo remove all global session variables and destroy the session, use Examplesession_start(); // remove all session variables // destroy the session Run example » PHP ExercisesAre PHP sessions are persistent by default?The default value of 0 means to end the session when the browser closes. You can override this value either directly in php. ini or set it in your application prior to starting the session using ini_set. Setting it to something greater than 0 will cause the session to live for that duration.
Where are PHP sessions stored by default?PHP Session Start
By default, session data is stored in the server's /tmp directory in files that are named sess_ followed by a unique alphanumeric string (the session identifier).
How long does PHP retain session variables by default?By default, session variables last until the user closes the browser. So; Session variables hold information about one single user, and are available to all pages in one application. Tip: If you need a permanent storage, you may want to store the data in a database.
Are PHP sessions secure?“Is a PHP session secure? PHP sessions are only as secure as your application makes them. PHP sessions will allow the client a pseudorandom string (“session ID”) for them to distinguish themselves with, but on the off chance that the string is intercepted by an attacker, the aggressor can imagine to be that client.
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