How can the EVA principle be applied to prevent issues with the header function in PHP?

The issue with the header function in PHP can be prevented by using the EVA principle, which stands for Escape, Validate, and Authenticate. This means that before using the header function, any user input should be properly escaped to prevent injection attacks, validated to ensure it meets the expected format, and authenticated to verify the user's permissions. 

$user_input = $_GET['input'];

// Escape user input
$escaped_input = htmlspecialchars($user_input);

// Validate user input
if (filter_var($escaped_input, FILTER_VALIDATE_URL)) {
    // Authenticate user permissions
    if ($authenticated) {
        header("Location: " . $escaped_input);
        exit();
    } else {
        echo "Unauthorized access.";
    }
} else {
    echo "Invalid input.";
}

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