What are the best practices for handling form submissions in PHP to prevent multiple submissions and spam?

To prevent multiple form submissions and spam in PHP, you can implement techniques such as using CSRF tokens, validating form data, and implementing CAPTCHA verification. These practices help ensure that each form submission is legitimate and unique. 

```php
session_start();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    if (!isset($_POST['csrf_token']) || $_POST['csrf_token'] !== $_SESSION['csrf_token']) {
        // Invalid CSRF token, handle accordingly
    } else {
        // Process form submission
        // Validate form data
        // Implement CAPTCHA verification
        // Prevent duplicate submissions
        unset($_SESSION['csrf_token']);
    }
}

$csrf_token = bin2hex(random_bytes(32));
$_SESSION['csrf_token'] = $csrf_token;
```
In this code snippet, we first start a session and generate a CSRF token to prevent CSRF attacks. We then check if the form submission method is POST and validate the CSRF token. If the token is valid, we process the form submission, validate the form data, implement CAPTCHA verification, and prevent duplicate submissions by unsetting the CSRF token after processing the form.

Keywords

Form submissions PHP prevent multiple submissions spam

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