How can server-side validation complement client-side validation in PHP to enhance security measures?

Client-side validation is performed on the user's device using JavaScript, which can be bypassed by malicious users. Server-side validation, on the other hand, is done on the server, ensuring that data is validated even if client-side validation fails. By implementing server-side validation in PHP, we can enhance security measures by double-checking user input before processing it. 

// Client-side validation in HTML form
<form method="post" action="process_form.php" onsubmit="return validateForm()">
    <input type="text" name="username" id="username">
    <input type="submit" value="Submit">
</form>

// Server-side validation in process_form.php
<?php
$username = $_POST['username'];

// Validate username on the server side
if (empty($username)) {
    echo "Username is required.";
} else {
    // Process the form data
    // Additional server-side validation can be added here
}
?>

Keywords

server-side validation client-side validation PHP security measures error types

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