我个人最喜欢以下解决方案:

using System.Security.Cryptography.X509Certificates;
using System.Net.Security;

．.． 然后在请求获取错误之前，执行以下操作

System.Net.ServicePointManager.ServerCertificateValidationCallback = delegate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };

这是在咨询卢克的解决方案后发现的

如果没有工作坏证书，当ServerCertificateValidationCallback返回true; 我的ServerCertificateValidationCallback代码:

ServicePointManager.ServerCertificateValidationCallback += delegate
{
    LogWriter.LogInfo("Проверка сертификата отключена, на уровне ServerCertificateValidationCallback");
    return true;
};

我的代码被阻止执行ServerCertificateValidationCallback:

     if (!(ServicePointManager.CertificatePolicy is CertificateValidation))
    {
        CertificateValidation certValidate = new CertificateValidation();
        certValidate.ValidatingError += new CertificateValidation.ValidateCertificateEventHandler(this.OnValidateCertificateError);
        ServicePointManager.CertificatePolicy = certValidate;
    }

OnValidateCertificateError功能:

private void OnValidateCertificateError(object sender, CertificateValidationEventArgs e)
{
    string msg = string.Format(Strings.OnValidateCertificateError, e.Request.RequestUri, e.Certificate.GetName(), e.Problem, new Win32Exception(e.Problem).Message);
    LogWriter.LogError(msg);
    //Message.ShowError(msg);
}

我禁用了CertificateValidation代码和ServerCertificateValidationCallback运行得很好

下面的代码片段将修复您正在调用的服务器上的SSL证书有问题的情况。例如，证书可能是自签名的，或者证书和服务器之间的主机名可能不匹配。

如果您正在调用您直接控制之外的服务器，这是危险的，因为您不能再确定您正在与您认为连接到的服务器通信。但是，如果您处理的是内部服务器，而获得“正确的”证书是不现实的，请使用以下命令告诉web服务忽略证书问题并勇敢地继续工作。

前两个使用lambda表达式，第三个使用常规代码。第一个接受任何证书。后两者至少检查证书中的主机名是否是您所期望的主机名。 ．.． 希望对你有帮助

//Trust all certificates
System.Net.ServicePointManager.ServerCertificateValidationCallback =
    ((sender, certificate, chain, sslPolicyErrors) => true);

// trust sender
System.Net.ServicePointManager.ServerCertificateValidationCallback
                = ((sender, cert, chain, errors) => cert.Subject.Contains("YourServerName"));

// validate cert by calling a function
ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(ValidateRemoteCertificate);

// callback used to validate the certificate in an SSL conversation
private static bool ValidateRemoteCertificate(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors policyErrors)
{
    bool result = cert.Subject.Contains("YourServerName");
    return result;
}

Luke写了一篇关于这方面的好文章。 非常直截了当。试试吧

卢克的解决方案

原因(引用自他的文章(含诅咒)) “. . 上面的代码的问题是，如果您的证书无效，它将无法工作。为什么我要发布到一个网页与无效的SSL证书?因为我很便宜，我不想付钱给Verisign或其他** *的人对我的测试箱进行认证，所以我自己签名了。当我发送请求时，我得到了一个可爱的例外:

System.Net.WebException 底层连接被关闭。无法与远程服务器建立信任关系。

我不知道你怎么想，但对我来说，这个异常看起来像是由我的代码中一个愚蠢的错误引起的，导致POST失败。所以我一直在寻找，调整，做各种奇怪的事情。只有在我谷歌了***n的东西，我发现遇到无效的SSL证书后的默认行为是抛出这个异常。 . .”

如果你使用的是Windows 2003，你可以这样做:

Open Microsoft Management Console (Start --> Run --> mmc.exe); Choose File --> Add/Remove Snap-in; In the Standalone tab, choose Add; Choose the Certificates snap-in, and click Add; In the wizard, choose the Computer Account, and then choose Local Computer. Press Finish to end the wizard; Close the Add/Remove Snap-in dialog; Navigate to Certificates (Local Computer) and choose a store to import: If you have the Root CA certificate for the company that issued the certificate, choose Trusted Root Certification Authorities; If you have the certificate for the server itself, choose Other People Right-click the store and choose All Tasks --> Import Follow the wizard and provide the certificate file you have; After that, simply restart IIS and try calling the web service again.

参考:http://www.outsystems.com/NetworkForums/ViewTopic.aspx?Topic=Web-Services: -Could-not-establish-trust-relationship-for-the-SSL / TLS -…

试试这个:

System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls12;

请注意，您必须至少使用4.5 .NET框架