.net core 2.0 HTTPS request fails using HttpClient 安全错误

最近.net core 项目中遇到一个问题,通过Httpclient 访问https的接口报错,错误如下:

WinHttpException: A security error occurred
    System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
    System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    System.Runtime.CompilerServices.ConfiguredTaskAwaitable+ConfiguredTaskAwaiter.GetResult()
    System.Net.Http.WinHttpHandler+<StartRequest>d__105.MoveNext()

HttpRequestException: An error occurred while sending the request.
    System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
    System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    System.Runtime.CompilerServices.ConfiguredTaskAwaitable+ConfiguredTaskAwaiter.GetResult()
    System.Net.Http.HttpClient+<FinishSendAsync>d__58.MoveNext()
    System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
    System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    System.Runtime.CompilerServices.TaskAwaiter.GetResult()
    MyApp.Web.Controllers.HomeController.Test() in HomeController.cs
        var response = client.GetAsync("https://someurl.com/api.php?arg1=some&arg2=test").GetAwaiter().GetResult();
    lambda_method(Closure , object , Object[] )
    Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker+<InvokeActionMethodAsync>d__27.MoveNext()

通过排查发现是.NETFramework 4.6包括一个新的安全特性，它阻止连接的不安全密码和散列算法。

可以通过下面的解决方案处理:

using (var handler = new HttpClientHandler())
{
    handler.ServerCertificateCustomValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true;
    handler.SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls11 | SslProtocols.Tls;
    using (HttpClient client = new HttpClient(handler))
    {
        string requestObjJson = requestObj.ToJson();
        var address = new Uri($"https://yourcompany.com/");
        string token = GetToken();
        client.BaseAddress = address;
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);
        var contentData = new StringContent(requestObjJson, System.Text.Encoding.UTF8, "application/json");
        using (var response = await client.PostAsync("yourcompany/api", contentData))
        {
            var content = response.Content.ReadAsStringAsync();
            var taskResult = content.Result;
            JObject resultObj = JObject.Parse(taskResult);
            return resultObj;
        }
    }
}

需要注意的是，对于.NET core 2.0，您需要使用HttpClientHandler而不是ServicePointManager.