我是这样做的:

using (HttpClient httpClient = new HttpClient())
{
   Dictionary<string, string> tokenDetails = null;
   var messageDetails = new Message { Id = 4, Message1 = des };
   HttpClient client = new HttpClient();
   client.BaseAddress = new Uri("http://localhost:3774/");
   var login = new Dictionary<string, string>
       {
           {"grant_type", "password"},
           {"username", "sa@role.com"},
           {"password", "lopzwsx@23"},
       };
   var response = client.PostAsync("Token", new FormUrlEncodedContent(login)).Result;
   if (response.IsSuccessStatusCode)
   {
      tokenDetails = JsonConvert.DeserializeObject<Dictionary<string, string>>(response.Content.ReadAsStringAsync().Result);
      if (tokenDetails != null && tokenDetails.Any())
      {
         var tokenNo = tokenDetails.FirstOrDefault().Value;
         client.DefaultRequestHeaders.Add("Authorization", "Bearer " + tokenNo);
         client.PostAsJsonAsync("api/menu", messageDetails)
             .ContinueWith((postTask) => postTask.Result.EnsureSuccessStatusCode());
      }
   }
}

这个you-tube视频帮了我大忙。请查看一下。 https://www.youtube.com/watch?v=qCwnU06NV5Q

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>();
}

如果您正在使用Visual Studio IISExpress调试模式并连接到HTTP端口而不是HTTPS端口，您可能会发现身份验证头被删除。

切换到SLL连接，它们将再次出现。

不确定原因，可能是设置重定向HTTP流量，导致身份验证被删除。

使用现有的库可能更容易。

例如，Identity Server 4中添加了下面的扩展方法 https://www.nuget.org/packages/IdentityModel/

 public static void SetBasicAuthentication(this HttpClient client, string userName, string password);
    //
    // Summary:
    //     Sets a basic authentication header.
    //
    // Parameters:
    //   request:
    //     The HTTP request message.
    //
    //   userName:
    //     Name of the user.
    //
    //   password:
    //     The password.
    public static void SetBasicAuthentication(this HttpRequestMessage request, string userName, string password);
    //
    // Summary:
    //     Sets a basic authentication header for RFC6749 client authentication.
    //
    // Parameters:
    //   client:
    //     The client.
    //
    //   userName:
    //     Name of the user.
    //
    //   password:
    //     The password.
    public static void SetBasicAuthenticationOAuth(this HttpClient client, string userName, string password);
    //
    // Summary:
    //     Sets a basic authentication header for RFC6749 client authentication.
    //
    // Parameters:
    //   request:
    //     The HTTP request message.
    //
    //   userName:
    //     Name of the user.
    //
    //   password:
    //     The password.
    public static void SetBasicAuthenticationOAuth(this HttpRequestMessage request, string userName, string password);
    //
    // Summary:
    //     Sets an authorization header with a bearer token.
    //
    // Parameters:
    //   client:
    //     The client.
    //
    //   token:
    //     The token.
    public static void SetBearerToken(this HttpClient client, string token);
    //
    // Summary:
    //     Sets an authorization header with a bearer token.
    //
    // Parameters:
    //   request:
    //     The HTTP request message.
    //
    //   token:
    //     The token.
    public static void SetBearerToken(this HttpRequestMessage request, string token);
    //
    // Summary:
    //     Sets an authorization header with a given scheme and value.
    //
    // Parameters:
    //   client:
    //     The client.
    //
    //   scheme:
    //     The scheme.
    //
    //   token:
    //     The token.
    public static void SetToken(this HttpClient client, string scheme, string token);
    //
    // Summary:
    //     Sets an authorization header with a given scheme and value.
    //
    // Parameters:
    //   request:
    //     The HTTP request message.
    //
    //   scheme:
    //     The scheme.
    //
    //   token:
    //     The token.
    public static void SetToken(this HttpRequestMessage request, string scheme, string token);

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

在net .core中，您可以使用Identity Server 4

var client = new HttpClient();
client.SetBasicAuthentication(userName, password);

or

var client = new HttpClient();
client.SetBearerToken(token);

参见https://github.com/IdentityModel/IdentityModel/blob/main/src/Client/Extensions/AuthorizationHeaderExtensions.cs