HttpClient授权标头格式无效

当我试图 GET 请求地址和授权值如下,我没有问题。

地址: http://example.com/xyz.svc/branches/?latitude=0&longitude=0&range=20000

标题键:授权

值:示例;foo公司

当我试着 HttpCLient 授权标头值的格式无效错误

我就是这样尝试的

HttpClient client = new HttpClient();

    string latitude = "0";
    string longitude = "0";
    string range = "2000";

    string uri = "/xyz.svc/branches/?latitude=0&longitude=0&range=20000;

    string value = "foo";

    client.BaseAddress = new Uri("http://example.com");
    client.DefaultRequestHeaders.Accept.Clear();
    client.DefaultRequestHeaders.Accept.Add(
        new MediaTypeWithQualityHeaderValue("application/json"));
    client.DefaultRequestHeaders.Add("Authorization", String.Format("example;{0}", value));

    HttpResponseMessage response = await client.GetAsync(uri);

    var responseJson = await response.Content.ReadAsStringAsync();

    Console.WriteLine(responseJson);

我做错了什么?