我在可移植类库上使用 HttpClient 收到 403

我有一个 PCL、WP 和 WinStore 项目。在 PCL 项目中，我有一个使用此方法的类：

    private async Task<string> GetIpAddress()
    {
        const string url = "http://www.ip-adress.com/";
        const string buscar = "<h3>Your IP address is:";

        var client = new HttpClient();
        var data = await client.GetStringAsync(url);
        if (data.IndexOf(buscar, StringComparison.Ordinal) <= -1) return;
        var IpAddress = data.Remove(0, data.IndexOf(buscar, StringComparison.Ordinal) + buscar.Length + 1);
        IpAddress = IpAddress.Remove(IpAddress.IndexOf("</h3>", StringComparison.Ordinal));
        return IpAddress;
    }

当我在 Windows Phone 项目上调用该方法时效果很好，但在 Windows Store 项目中则不然。相反，我收到此错误消息：

看来你需要凭证并指向 api，这就是为什么它是“Forbiden”的原因

尝试像浏览器一样调用它：来自另一个问题“HttpClient 像浏览器一样请求"

void Main()
{

    GetIP("http://www.ip-adress.com/");

}

async void GetIP(string url){
    try{
    "Looking Up".Dump("OK");
    var x = await  GetResponse(url);
    x.Dump();
    }
    catch(Exception e){
        e.Dump("Problems:");
    }
}

private static async Task<string> GetResponse(string url)
{
    var httpClient = new HttpClient();

    httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Accept", "text/html,application/xhtml+xml,application/xml");
    httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Accept-Encoding", "gzip, deflate");
    httpClient.DefaultRequestHeaders.TryAddWithoutValidation("User-Agent", "Mozilla/5.0 (Windows NT 6.2; WOW64; rv:19.0) Gecko/20100101 Firefox/19.0");
    httpClient.DefaultRequestHeaders.TryAddWithoutValidation("Accept-Charset", "ISO-8859-1");

    var response = await httpClient.GetAsync(new Uri(url));

    response.EnsureSuccessStatusCode();
    using (var responseStream = await response.Content.ReadAsStreamAsync())
    //using (var decompressedStream = new System.IO.Compression.GZipStream(responseStream, CompressionMode.Decompress))
    using (var streamReader = new StreamReader(responseStream))
    {
        return streamReader.ReadToEnd();
    }
}

//注意：我注释掉了压缩，