下面是如何为请求设置自定义cookie值:

var baseAddress = new Uri("http://example.com");
var cookieContainer = new CookieContainer();
using (var handler = new HttpClientHandler() { CookieContainer = cookieContainer })
using (var client = new HttpClient(handler) { BaseAddress = baseAddress })
{
    var content = new FormUrlEncodedContent(new[]
    {
        new KeyValuePair<string, string>("foo", "bar"),
        new KeyValuePair<string, string>("baz", "bazinga"),
    });
    cookieContainer.Add(baseAddress, new Cookie("CookieName", "cookie_value"));
    var result = await client.PostAsync("/test", content);
    result.EnsureSuccessStatusCode();
}

在大多数情况下，公认的答案是正确的方法。但是，在某些情况下，您需要手动设置cookie报头。通常情况下，如果你设置了一个“Cookie”报头，它会被忽略，但这是因为HttpClientHandler默认为Cookie使用它的CookieContainer属性。如果你禁用了，那么通过设置UseCookies为false，你可以手动设置cookie头，它们将出现在请求中，例如。

var baseAddress = new Uri("http://example.com");
using (var handler = new HttpClientHandler { UseCookies = false })
using (var client = new HttpClient(handler) { BaseAddress = baseAddress })
{
    var message = new HttpRequestMessage(HttpMethod.Get, "/test");
    message.Headers.Add("Cookie", "cookie1=value1; cookie2=value2");
    var result = await client.SendAsync(message);
    result.EnsureSuccessStatusCode();
}

在这个问题上花了几个小时后，上面的答案都对我没有帮助，所以我找到了一个非常有用的工具。

首先，我使用Telerik的Fiddler 4详细研究了我的Web请求

其次，我发现了这个有用的Fiddler插件:

https://github.com/sunilpottumuttu/FiddlerGenerateHttpClientCode

它将为您生成c#代码。一个例子是:

        var uriBuilder = new UriBuilder("test.php", "test");
        var httpClient = new HttpClient();


        var httpRequestMessage = new HttpRequestMessage(HttpMethod.Post, uriBuilder.ToString());



        httpRequestMessage.Headers.Add("Host", "test.com");
        httpRequestMessage.Headers.Add("Connection", "keep-alive");
     //   httpRequestMessage.Headers.Add("Content-Length", "138");
        httpRequestMessage.Headers.Add("Pragma", "no-cache");
        httpRequestMessage.Headers.Add("Cache-Control", "no-cache");
        httpRequestMessage.Headers.Add("Origin", "test.com");
        httpRequestMessage.Headers.Add("Upgrade-Insecure-Requests", "1");
    //    httpRequestMessage.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
        httpRequestMessage.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36");
        httpRequestMessage.Headers.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8");
        httpRequestMessage.Headers.Add("Referer", "http://www.translationdirectory.com/");
        httpRequestMessage.Headers.Add("Accept-Encoding", "gzip, deflate");
        httpRequestMessage.Headers.Add("Accept-Language", "en-GB,en-US;q=0.9,en;q=0.8");
        httpRequestMessage.Headers.Add("Cookie", "__utmc=266643403; __utmz=266643403.1537352460.3.3.utmccn=(referral)|utmcsr=google.co.uk|utmcct=/|utmcmd=referral; __utma=266643403.817561753.1532012719.1537357162.1537361568.5; __utmb=266643403; __atuvc=0%7C34%2C0%7C35%2C0%7C36%2C0%7C37%2C48%7C38; __atuvs=5ba2469fbb02458f002");


        var httpResponseMessage = httpClient.SendAsync(httpRequestMessage).Result;

        var httpContent = httpResponseMessage.Content;
        string result = httpResponseMessage.Content.ReadAsStringAsync().Result;

注意，我不得不注释掉两行，因为这个插件还不是完全完美的，但它仍然完成了工作。

免责声明:我与Telerik或插件作者没有任何联系或认可。

对我来说，简单的解决方案是在HttpRequestMessage对象中设置cookie。

protected async Task<HttpResponseMessage> SendRequest(HttpRequestMessage requestMessage, CancellationToken cancellationToken = default(CancellationToken))
{
    requestMessage.Headers.Add("Cookie", $"<Cookie Name 1>=<Cookie Value 1>;<Cookie Name 2>=<Cookie Value 2>");

    return await _httpClient.SendAsync(requestMessage, cancellationToken).ConfigureAwait(false);
}

我遇到过类似的问题，对于我的AspNetCore 3.1应用程序，这个问题的其他答案都不起作用。我发现在我的Startup.cs中配置一个名为HttpClient的程序，并使用Cookie头的头传播，效果非常好。这也避免了对你的处理者和客户的适当处置的所有担忧。注意，如果请求cookie的传播不是你所需要的(抱歉，Op)，你可以在配置客户端工厂时设置自己的cookie。

我使用了微软的这个指南-在ASP中使用IHttpClientFactory进行HTTP请求。网络核心 报头传播将在本节-报头传播中间件中介绍

使用IServiceCollection配置服务

services.AddHttpClient("MyNamedClient").AddHeaderPropagation();
services.AddHeaderPropagation(options =>
{
    options.Headers.Add("Cookie");
});

使用IApplicationBuilder进行配置

builder.UseHeaderPropagation();

将IHttpClientFactory注入到您的控制器或中间件中。 使用var client = clientFactory.CreateClient("MyNamedClient")创建客户端;

如果您想要使用HttpClient发送一个要求用户登录的请求，这意味着您需要执行登录过程，然后接收cookie并将这些cookie发送给需要登录的请求。

我在测试一个名为IsLoggedIn的动作时做到了这一点。该操作检查用户是否使用HttpRequest中的cookie进行了登录。

我在测试这个动作时所做的是:

                string Login = JsonConvert.SerializeObject(new LoginViewModel()
                {
                    Email = userFromDb.Email,
                    Password = "fdfdf@2239",
                    RememberMe = false
                }); ;
                StringContent LoginhttpContent = new(Login, Encoding.UTF8, "application/json");
                var Login_response = await _httpClient.PostAsync(HelperFunctions.getUrl(HelperFunctions.AcctounController.name, HelperFunctions.AcctounController.Login), LoginhttpContent);
                Assert.Equal(HttpStatusCode.OK, Login_response.StatusCode);
    
                //receive cookies from the login response
                var cookies = Login_response.Headers.GetValues(HeaderNames.SetCookie);
                 //Add the cookies to the DefaultRequestHeaders of the _httpClient
                _httpClient.DefaultRequestHeaders.Add("Cookie",cookies);
                var IsLoggedIn_response = await _httpClient.GetAsync(HelperFunctions.getUrl(HelperFunctions.AcctounController.name, HelperFunctions.AcctounController.IsLoggedIn));
                Assert.Equal("true",IsLoggedIn_response.Content.ReadAsStringAsync().Result);