HttpClient无法创建SSL / TLS安全通道

Question

嗨，当我向我们的api发出获取请求时，我收到了错误消息“请求已中止：无法创建SSL / TLS安全通道”。

我尝试将ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12添加到我的代码中，因为这是如何解决该问题的最受欢迎的答案。它可以在我的本地主机上运行，​​但不能在我们的服务器上运行。

我已经使用IISCrypto在我们的服务器上进行了检查，以确保在我们的服务器上启用了TLS 1.2。在Web服务器上的Windows中也启用了“强密码模式”。

        string baseURI = "";
        string token = "";
        ServicePointManager.Expect100Continue = true;
        ServicePointManager.DefaultConnectionLimit = 9999;
        ServicePointManager.ServerCertificateValidationCallback = Validate;
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
        HttpClient newClient = new HttpClient();
        var authValue = new AuthenticationHeaderValue("Bearer", token);          
        newClient.DefaultRequestHeaders.Authorization = authValue;

        try
        {
            using (HttpResponseMessage post = await newClient.GetAsync(String.Format("{0}{1}", baseURI, absoluteURI)).ConfigureAwait(false))
            {
                try
                {
                    post.EnsureSuccessStatusCode();
                    var read = await post.Content.ReadAsStringAsync().ConfigureAwait(false);
                    apiPost = post;
                    apiResponse = read.ToString();
                    successful = true;
                }
                catch (HttpRequestException hex)
                {
                    apiResponse = post.StatusCode.ToString();
                    successful = false;
                    Email.ErrorEmail("-1", "-1", "Mattermost API Error", hex, apiResponse);
                }
            }
        }
        catch (Exception ex)
        {
            Email.ErrorEmail("-1", "-1", "Mattermost API Error", ex, apiResponse);
        }            
    }

    public static bool Validate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
    {
        if (sslPolicyErrors != SslPolicyErrors.None)
        {
            return false;
        }
        return true;
    }