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How to Share Session Variables Between PHP Files for Secure CSRF Token Handling

June 12, 2024 3 Min read PHP

In this tutorial, we will learn how to share session variables between PHP files, specifically focusing on handling a CSRF (Cross-Site Request Forgery) token securely. By the end of this tutorial, you will understand how to set a session variable in one PHP file and access it in another.

Prerequisites

  • Basic knowledge of PHP
  • Understanding of web sessions and how they work
  • A local server environment like XAMPP, WAMP, or a remote server with PHP installed

Step 1: Setting Up Your Environment

Ensure you have a web server with PHP installed and running. If you’re working locally, tools like XAMPP or WAMP will help you set up a PHP environment quickly.

Step 2: Creating the First PHP File (A.php)

This file will initialize the session and set the CSRF token.

  1. Start the session: This is crucial as sessions need to be started in any PHP file that accesses or modifies session variables.
  2. Generate a CSRF token: A secure random token is necessary to protect against CSRF attacks.
  3. Store the CSRF token in the session: This allows us to access the token from other PHP files.

Create a file named A.php and add the following code:

<?php
// Start the session
session_start();

// Generate a CSRF token
$csrf_token = bin2hex(random_bytes(32));

// Register the CSRF token in the session
$_SESSION['csrf_token_registration'] = $csrf_token;

echo "CSRF token has been set.";
?>

Step 3: Creating the Second PHP File (B.php)

This file will retrieve and use the CSRF token set in the session.

  1. Start the session: This is necessary to access session variables.
  2. Check if the CSRF token is set: Ensure the token exists before trying to use it.
  3. Retrieve and display the CSRF token: Access the token stored in the session and use it as needed.

Create a file named B.php and add the following code:

<?php
// Start the session
session_start();

// Check if the CSRF token is set
if (isset($_SESSION['csrf_token_registration'])) {
    $csrf_token = $_SESSION['csrf_token_registration'];
    echo "CSRF Token: " . $csrf_token;
} else {
    echo "CSRF token is not set.";
}
?>

Step 4: Testing the Implementation

  1. Run A.php: Open your browser and navigate to A.php (e.g., http://localhost/A.php). You should see a message saying, “CSRF token has been set.”
  2. Run B.php: Now, navigate to B.php (e.g., http://localhost/B.php). You should see the CSRF token displayed on the screen.

Explanation

  • Starting the session: session_start() initializes the session, making session variables accessible in the script.
  • Setting the session variable: In A.php, we generate a secure CSRF token using bin2hex(random_bytes(32)) and store it in the session array $_SESSION['csrf_token_registration'].
  • Accessing the session variable: In B.php, we check if $_SESSION['csrf_token_registration'] is set to ensure the token exists before trying to use it.

Tags:

  • PHP session variables
  • CSRF token handling in PHP
  • Secure session management PHP
  • Share session variables PHP
  • PHP cross-site request forgery prevention
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