How can PHP sessions be used to prevent form resubmission and spam?

To prevent form resubmission and spam, PHP sessions can be used to track whether a form has already been submitted by a user. By setting a session variable upon form submission and checking for its existence before processing the form data, duplicate submissions can be avoided. Additionally, implementing CAPTCHA or other spam prevention techniques can further enhance form security. 

<?php
session_start();

if(isset($_SESSION['form_submitted'])) {
    // Form has already been submitted
    // Redirect or display an error message
} else {
    // Process form data
    // Set session variable to prevent resubmission
    $_SESSION['form_submitted'] = true;
}
?>

Keywords

PHP sessions form resubmission spam prevention session variables CSRF protection

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