protected function Require401Authentication(IAuthenticatable $authenticatable, $realm = "Login Required", $qs_username_field = "", $qs_password_field = "")
	{
		require_once("verysimple/Authentication/Auth401.php");
		
		$user = $this->Get401Authentication($authenticatable,$qs_username_field, $qs_password_field);

		// we only want to output 401 headers if the user is not already authenticated
		if (!$user)
		{
			if( $this->Get401AuthUsername($qs_username_field) )
			{
				// a username was provided, which means login failed
				Auth401::OutputHeaders("Invalid Login");
			}
			else
			{
				// no username provided, which means prompt for username
				Auth401::OutputHeaders($realm);
			}
		}
	}