How can variables be securely passed to external websites in PHP?

To securely pass variables to external websites in PHP, it is recommended to use parameterized queries when making database queries to prevent SQL injection attacks. Additionally, you can use functions like htmlspecialchars() or htmlentities() to sanitize user input before sending it to external websites. It is also important to validate and sanitize all user input to prevent cross-site scripting (XSS) attacks.

// Example of securely passing variables to an external website
$variable = $_POST['variable']; // Get the variable from a form submission

// Sanitize the variable before passing it to the external website
$secure_variable = htmlspecialchars($variable);

// Pass the secure variable to the external website
$url = "https://www.externalwebsite.com?variable=" . $secure_variable;
header("Location: $url");
exit();