if (!isset($_SERVER['PHP_AUTH_USER'])) 
  {
   header('WWW-Authenticate: Basic realm="My Realm"');
   header('HTTP/1.0 401 Unauthorized');
   echo 'You must have a valid user name and password to login!';
   exit;
  } else 
  	{
		if	( ($_SERVER['PHP_AUTH_USER']=="auser") && 
			($_SERVER['PHP_AUTH_PW']=="apassword") )
		{
//			echo "<p>excellent user name and password !</p>";
		} else {
				   header('WWW-Authenticate: Basic realm="My Realm"');
				   header('HTTP/1.0 401 Unauthorized');
				   echo 'You must have a valid user name and password to login!';
				   exit;
				}
    }