PHP从Linkedin获取数据

这是我试图用于从LinkedIN获取数据的一段代码。我已经有了访问令牌。我只需要LinkedIN的用户id:

        $params = array(
            'oauth2_access_token' => $authToken,
            'format' => 'json',
        );

        $url = 'https://api.linkedin.com/v1/people/~:(id)?' . http_build_query($params);
        $context = stream_context_create(
            array('http' =>
                array(
                    'method' => "GET",
                )
            )
        );
        $response = file_get_contents($url, false, $context);
        return $response;

但是它返回

failed to open stream: HTTP request failed! HTTP/1.0 401 Unauthorized

访问令牌未过期。我做错了什么?