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);
        }
    }

使用System.Net.Http程序集的AuthenticationHeaderValue类

public AuthenticationHeaderValue(
    string scheme,
    string parameter
)

我们可以像这样设置或更新httpclient现有的授权头:

httpclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", TokenResponse.AccessToken);

6年过去了，但为了帮助别人，我加了这个。

https://www.codeproject.com/Tips/996401/Authenticate-WebAPIs-with-Basic-and-Windows-Authen

var authenticationBytes = Encoding.ASCII.GetBytes("<username>:<password>");
using (HttpClient confClient = new HttpClient())
{
  confClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", 
         Convert.ToBase64String(authenticationBytes));
  confClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(Constants.MediaType));  
  HttpResponseMessage message = confClient.GetAsync("<service URI>").Result;
  if (message.IsSuccessStatusCode)
  {
    var inter = message.Content.ReadAsStringAsync();
    List<string> result = JsonConvert.DeserializeObject<List<string>>(inter.Result);
  }
}

我在寻找一个好的方法来处理这个问题，我也在考虑同样的问题。希望这个答案能帮助到每个和我一样有同样问题的人。

using (var client = new HttpClient())
{
    var url = "https://www.theidentityhub.com/{tenant}/api/identity/v1";
    client.DefaultRequestHeaders.Add("Authorization", "Bearer " + accessToken);
    var response = await client.GetStringAsync(url);
    // Parse JSON response.
    ....
}

参考来自https://www.theidentityhub.com/hub/Documentation/CallTheIdentityHubApi

Oauth流程是复杂的，总是有一个或另一个错误的空间。 我的建议是始终使用样板代码和一组用于OAuth身份验证流的库。这会让你的生活更轻松。

下面是库集的链接。用于。net的OAuth库

BaseWebApi.cs

public abstract class BaseWebApi
{
    //Inject HttpClient from Ninject
    private readonly HttpClient _httpClient;
    public BaseWebApi(HttpClient httpclient)
    {
        _httpClient = httpClient;
    }

    public async Task<TOut> PostAsync<TOut>(string method, object param, Dictionary<string, string> headers, HttpMethod httpMethod)
    {
        //Set url

        HttpResponseMessage response;
        using (var request = new HttpRequestMessage(httpMethod, url))
        {
            AddBody(param, request);
            AddHeaders(request, headers);
            response = await _httpClient.SendAsync(request, cancellationToken);
        }

        if(response.IsSuccessStatusCode)
        {
             return await response.Content.ReadAsAsync<TOut>();
        }
        //Exception handling
    }

    private void AddHeaders(HttpRequestMessage request, Dictionary<string, string> headers)
    {
        request.Headers.Accept.Clear();
        request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        if (headers == null) return;

        foreach (var header in headers)
        {
            request.Headers.Add(header.Key, header.Value);
        }
    }

    private static void AddBody(object param, HttpRequestMessage request)
    {
        if (param != null)
        {
            var content = JsonConvert.SerializeObject(param);
            request.Content = new StringContent(content);
            request.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        }
    }

SubWebApi.cs

public sealed class SubWebApi : BaseWebApi
{
    public SubWebApi(HttpClient httpClient) : base(httpClient) {}

    public async Task<StuffResponse> GetStuffAsync(int cvr)
    {
        var method = "get/stuff";
        var request = new StuffRequest 
        {
            query = "GiveMeStuff"
        }
        return await PostAsync<StuffResponse>(method, request, GetHeaders(), HttpMethod.Post);
    }
    private Dictionary<string, string> GetHeaders()
    {
        var headers = new Dictionary<string, string>();
        var basicAuth = GetBasicAuth();
        headers.Add("Authorization", basicAuth);
        return headers;
    }

    private string GetBasicAuth()
    {
        var byteArray = Encoding.ASCII.GetBytes($"{SystemSettings.Username}:{SystemSettings.Password}");
        var authString = Convert.ToBase64String(byteArray);
        return $"Basic {authString}";
    }
}