我偶然发现了这条旧线索。我遇到的问题是我知道使用静态HttpClient，但是我的令牌需要每59分钟刷新一次。

所以我可以使用HttpClientFactory，但是因为我的一个项目仍然在. net 4.8中，我创建了一个从HttpClient继承的类，所以我在所有项目中都有类似的代码。需要一个秘密才能获得令牌(我使用identityserver4)。

然后我将它设置为DI中的单例(我在这里使用Ninject):

Bind<MyHttpClient>().ToMethod(c =>
{
    var accessKey = ConfigurationManager.AppSettings["AccessKey"];

    var client = new MyHttpClient(accessKey)
    {
        BaseAddress = new Uri(MyUrls.MyApiBaseUrl)
    };

    client.DefaultRequestHeaders.Accept.Clear();
    client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));

    return client;
}).InSingletonScope();

然后是类本身——以它用来访问的API命名:

public class MyHttpClient : BaseHttpClient
{
     private static readonly HttpClient _authHttpClient = new HttpClient();
     private string _secret;

     public MyHttpClient(string secret)
     {
         _secret = secret;
     }

    /// <summary>
    /// Add the token to each and every request, cached for 1 minute less than the token's lifetime
    /// </summary>
    /// <param name="request"></param>
    /// <param name="cancellationToken"></param>
    /// <returns></returns>
    /// <exception cref="Exception"></exception>
    public override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();

        var cacheSeconds = 3600 - 60; // Default of 59 minutes

        var token = CacheHelper<string>.Get("MyToken", cacheSeconds * 60, () =>
        {
            var authorityUrl = MyUrls.AuthServerUrl;

            // discover endpoints from metadata
            DiscoveryDocumentResponse disco;
            disco = _authHttpClient.GetDiscoveryDocumentAsync(authorityUrl).Result;
            if (disco.IsError)
            {
                throw new Exception("Error getting discovery document: " + disco.Error);
            }

            // request token
            var tokenResponse = _authHttpClient.RequestClientCredentialsTokenAsync(new ClientCredentialsTokenRequest
            {
                Address = disco.TokenEndpoint,

                ClientId = "myapp",
                ClientSecret = _secret,
                Scope = "myapi"
            }).Result;

            if (tokenResponse.IsError)
            {
                throw new Exception("Error getting token: " + tokenResponse.Error);
            }

            if (tokenResponse.ExpiresIn < cacheSeconds + 60)
            {
                throw new Exception($"Token expires in {tokenResponse.ExpiresIn}s, which is less than {cacheSeconds + 60}");
            }

            if (tokenResponse.ExpiresIn > cacheSeconds + 60)
            {
                Log.Warn().Message($"Token expiry in {tokenResponse.ExpiresIn}s, which is greater than {cacheSeconds}").Write();
            }

            return tokenResponse.AccessToken;
        });

        // THIS IS THE BIT - Assign this inside a SendAsync override and you are done!
        request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
        return base.SendAsync(request, cancellationToken);
    }

}

最后为了完整起见，我的CacheHelper类看起来是这样的:

public static class CacheHelper<T>
{
    private static readonly object _locker = new object();

    public static T Get(string cacheName, int cacheTimeoutSeconds, Func<T> func)
    {
        var obj = MemoryCache.Default.Get(cacheName, null);
        if (obj != null) return (T)obj;

        lock (_locker)
        {
            obj = MemoryCache.Default.Get(cacheName, null);
            if (obj == null)
            {
                obj = func();
                var cip = new CacheItemPolicy
                {
                    AbsoluteExpiration = new DateTimeOffset(DateTime.UtcNow.AddSeconds(cacheTimeoutSeconds))
                };
                MemoryCache.Default.Set(cacheName, obj, cip);
            }
        }

        return (T)obj;
    }
}

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

use UTF8选项

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

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。

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);

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);