public function authorize_url($client_id, $redirect_uri, $scope = 'AdministerAccount', $state = false) {
		$qs = 'type=web_server';
		$qs .= '&client_id=' . urlencode($client_id);
		$qs .= '&redirect_uri=' . urlencode($redirect_uri);
		$qs .= '&scope=' . urlencode($scope);
		if ($state)
			$qs .= '&state=' . urlencode($state);
		return self::OAUTH_URL . '?' . $qs;
	}