对于性能和端口耗尽问题，重用HttpClient实例是一个很好的实践，而且因为没有一个答案给出了这个解决方案(甚至会把你引向糟糕的实践:)，所以我在这里放了一个链接，指向我对类似问题的回答:

https://stackoverflow.com/a/40707446/717372

一些关于如何正确使用HttpClient的源代码:

https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/ https://blogs.msdn.microsoft.com/alazarev/2017/12/29/disposable-finalizers-and-httpclient/

如果你想重用HttpClient，建议不要使用DefaultRequestHeaders，因为它们是用来发送每个请求的。

你可以试试这个:

var requestMessage = new HttpRequestMessage
    {
        Method = HttpMethod.Post,
        Content = new StringContent("...", Encoding.UTF8, "application/json"),
        RequestUri = new Uri("...")
    };

requestMessage.Headers.Authorization = new AuthenticationHeaderValue("Basic", 
    Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes($"{user}:{password}")));

var response = await _httpClient.SendAsync(requestMessage);

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);

对于现在(2021年)找到这个旧线程的人，请看看这个关于HttpClientFactory的文档，它是可注入的，也会在每个请求上重新运行，避免过期的令牌，这将使它对承载令牌，生成的客户端，池等有用。

TL;DR:使用HttpClientFactory和一个DelegatingHandler，它将作为与您配置的客户端的所有外发请求的中间件。

这就是我如何为Azure身份添加我的承载者(由Azure管理)，但你当然可以获得你想要的令牌;

using Microsoft.Azure.Services.AppAuthentication;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

public class BearerTokenHandler : DelegatingHandler
    {
        public BearerTokenHandler(AzureServiceTokenProvider tokenProvider, string resource)
        {
            TokenProvider = tokenProvider;
            Resource = resource;
        }

        public AzureServiceTokenProvider TokenProvider { get; }
        public string Resource { get; }

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            if (!request.Headers.Contains("Authorization"))
            {
                // Fetch your token here
                string token = await TokenProvider.GetAccessTokenAsync(Resource);
                request.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);
            }

            return await base.SendAsync(request, cancellationToken);
        }
    }

我在Startup中这样配置我的类型化客户端(用NSwag生成);

   var accessTokenProvider = new AzureServiceTokenProvider("<your-connection-string-for-access-token-provider>");

  builder.Services.AddHttpClient<IOrdersClient, OrdersClient>().ConfigureHttpClient(async conf =>
            {
                conf.BaseAddress = new Uri("<your-api-base-url>");
            }).AddHttpMessageHandler(() => new BearerTokenHandler(accessTokenProvider, "https://your-azure-tenant.onmicrosoft.com/api"));

然后你可以在任何你喜欢的地方注入你的IOrdersClient，所有的请求都会有承载者。

对于性能和端口耗尽问题，重用HttpClient实例是一个很好的实践，而且因为没有一个答案给出了这个解决方案(甚至会把你引向糟糕的实践:)，所以我在这里放了一个链接，指向我对类似问题的回答:

https://stackoverflow.com/a/40707446/717372

一些关于如何正确使用HttpClient的源代码:

https://aspnetmonsters.com/2016/08/2016-08-27-httpclientwrong/ https://blogs.msdn.microsoft.com/alazarev/2017/12/29/disposable-finalizers-and-httpclient/

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