What are some best practices for implementing a reload prevention mechanism in PHP forms?

When submitting a form multiple times, users can accidentally trigger multiple actions or create duplicate entries in a database. To prevent this, a reload prevention mechanism can be implemented in PHP forms. One common approach is to use a token system where a unique token is generated and stored in a session variable. Upon form submission, the token is checked to ensure that the form is only processed once. 

```php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    if (!isset($_POST['token']) || $_POST['token'] !== $_SESSION['token']) {
        // Invalid token, do not process form
        die('Form submission error');
    }

    // Process form data

    // Reset token to prevent duplicate submissions
    unset($_SESSION['token']);
}

// Generate and store a unique token
$token = bin2hex(random_bytes(16));
$_SESSION['token'] = $token;
```
This code snippet demonstrates how to implement a reload prevention mechanism using a token system in PHP forms. It generates a unique token using `random_bytes()` and stores it in a session variable. Upon form submission, the token is checked to ensure that the form is only processed once. If the token is invalid or missing, the form submission is rejected.

Keywords

CSRF protection form validation session tokens HTTP POST method input sanitization

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