Código PHP:
if (!($_SERVER['PHP_AUTH_USER'] == $config['admin_username'] && $_SERVER['PHP_AUTH_PW'] == $config['admin_password'])) {
header("WWW-Authenticate: Basic realm=\"Administration\"");
header("HTTP/1.0 401 Unauthorized");
echo "Authentication failure. Click <a href=\"index.php\"><b>here</b></a> to login again.\n</center>\n</div>\n</body>\n</html>";
exit;
}