HOW CAN WE IMPLMENT CSRF TOKEN FROM SCRATCH

 Implementing CSRF (Cross-Site Request Forgery) protection from scratch involves generating and validating tokens to prevent unauthorized requests. Here's a basic outline of how you can implement CSRF token protection manually:

1. Generate a CSRF Token:

   • Create a function to generate a random CSRF token. This token should be unique for each session and request.
   • Store the generated token in the session for the user. In PHP, you can store it in the $_SESSION superglobal.

2. Insert CSRF Token into Forms:

   • For each form in your application that performs sensitive actions (e.g., submitting data, updating records), include a hidden input field to hold the CSRF token value.
   • When rendering the form, insert the CSRF token value from the session into the hidden input field.

3. Validate CSRF Token on Form Submission:

   • When a form is submitted, extract the CSRF token value from the form data.
   • Compare the extracted token value with the token value stored in the session for the current user.
   • If the token values match, process the form submission. Otherwise, reject the request as a potential CSRF attack.

Here's an example of how you might implement these steps in PHP:

1. Generate CSRF Token (csrf_token.php)

php
<?php
session_start();

function generateCsrfToken() {
    return bin2hex(random_bytes(32)); // Generate a 64-character hexadecimal token
}

$_SESSION['csrf_token'] = generateCsrfToken();

2. Insert CSRF Token into Form (form.php)

php
<?php
session_start();

// Include the CSRF token generation file
include 'csrf_token.php';

// Use the generated CSRF token in your form
$csrfToken = $_SESSION['csrf_token'];
?>
<form action="process_form.php" method="POST">
    <!-- Other form fields -->
    <input type="hidden" name="csrf_token" value="<?php echo $csrfToken; ?>">
    <button type="submit">Submit</button>
</form>

3. Validate CSRF Token on Form Submission (process_form.php)

php
<?php
session_start();

// Validate CSRF token
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $submittedToken = $_POST['csrf_token'] ?? '';
    $storedToken = $_SESSION['csrf_token'] ?? '';

    if (hash_equals($storedToken, $submittedToken)) {
        // CSRF token is valid, process the form submission
        // Perform necessary actions here
        echo "CSRF Token Valid";
    } else {
        // CSRF token mismatch, reject the request
        echo "CSRF Token Invalid";
    }
} else {
    // Handle invalid request method
    echo "Invalid Request Method";
}

This is a basic implementation to get you started. In a real-world application, you would enhance this implementation by adding additional security measures such as token expiration