Send headers to prompt for basic HTTP authentication.
Source Code
if (!isset($_SERVER['PHP_AUTH_USER'])) {
header('WWW-Authenticate: Basic realm="My Realm"');
header('HTTP/1.0 401 Unauthorized');
echo 'Text to send if user hits Cancel button';
exit;
} else {
echo "Hello {$_SERVER['PHP_AUTH_USER']}.
";
echo "You entered {$_SERVER['PHP_AUTH_PW']} as your password.
";
}