Basic Authentication

$username = $_SERVER['PHP_AUTH_USER'];
$password = $_SERVER['PHP_AUTH_PW'];
if ($username == 'admin' && $password == 'secret') {
    echo 'Authentication successful.';
} else {
    header('WWW-Authenticate: Basic realm="Restricted Area"');
    header('HTTP/1.0 401 Unauthorized');
    echo 'Authentication failed.';
    exit;
}