static async Task<AccessToken> GetToken()
{
        string clientId = "XXX";
        string clientSecret = "YYY";
        string credentials = String.Format("{0}:{1}", clientId, clientSecret);

        using (var client = new HttpClient())
        {
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(Encoding.UTF8.GetBytes(credentials)));
            List<KeyValuePair<string, string>> requestData = new List<KeyValuePair<string, string>>();
            requestData.Add(new KeyValuePair<string, string>("grant_type", "client_credentials"));
            FormUrlEncodedContent requestBody = new FormUrlEncodedContent(requestData);
            var request = await client.PostAsync("https://accounts.spotify.com/api/token", requestBody);
            var response = await request.Content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<AccessToken>(response);
        }
    }

方法是这样的，

httpClient.DefaultRequestHeaders.Authorization =
    new AuthenticationHeaderValue("Bearer", "Your Oauth token");

我建议你:

HttpClient.DefaultRequestHeaders.Add("Authorization", "Bearer <token>");

然后你可以这样使用它:

var response = await client.GetAsync(url);
if (response.IsSuccessStatusCode)
{
    responseMessage = await response.Content.ReadAsAsync<ResponseMessage>();
}

use UTF8选项

request.DefaultRequestHeaders.Authorization = 
new AuthenticationHeaderValue(
    "Basic", Convert.ToBase64String(
        System.Text.Encoding.UTF8.GetBytes(
           $"{yourusername}:{yourpwd}")));

我在设置不记名代币

httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);

它在一个端点上起作用，但在另一个端点上不起作用。问题是我在"持票人"上用了小写b。改变后，现在它工作的两个api的我正在击中。如果你甚至不把它看作是寻找针的干草堆之一，这是一件很容易错过的事情。

一定要有“持票人”，要有资本。

request.DefaultRequestHeaders.Authorization = 
    new AuthenticationHeaderValue(
        "Basic", Convert.ToBase64String(
            System.Text.ASCIIEncoding.ASCII.GetBytes(
               $"{yourusername}:{yourpwd}")));