带有HTTPS的WebClient.DownloadString“验证或解密失败”

Question

我正在使用Windows 10上的Unity Engine（2017.2.0f3）创建一个游戏，我试图从网页上获取html。据我所知，Unity使用“Mono”C＃编译器和运行时v2.0（根据在mono --version中运行UnityEditorDataMonoin的结果），还使用v5.0.1（根据在mono --version中运行UnityEditorDataMonoBleedingEdgein的结果）。我目前正在使用HTML Agility Pack进行解析。当试图访问HTTP安全网站时，例如dictionary.com，一切都按预期工作，但无论我做什么，我都无法访问HTTPS安全网站，例如urbandictionary.com（编辑：显然，问题是特定于此网站的，因为使用mozroots导入证书后，可以访问github.com），并始终收到异常：TlsException: The authentication or decryption has failed.我知道HTML Agility Pack不支持HTTPS，并根据this answer编写了我的代码。我已经尝试过here和here描述的解决方案，但无济于事。我试过运行mozroots，我位于PathTo/Unity/Editor/Data/MonoBleedingEdge/lib/mono/4.5/mozroots，使用--import，--sync和--quiet标志，但同样的异常被抛出（如果这确实有效，我对它的可移植性持怀疑态度，但也许我可以实现自己的mozroots的版本，如评论所建议的）。此外，我被告知Unity使用的Mono版本不支持TLS 1.2，这是有问题的。如果没有解决此问题的方法，是否有任何解决方法？

注意：为清晰起见删节

class MyWebClient : WebClient
{
    protected override WebRequest GetWebRequest(Uri address)
    {
        HttpWebRequest request = base.GetWebRequest(address) as HttpWebRequest;
        request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
        return request;
    }
}

class GetHtml
{
    public static void Get(string url)
    {
        string documentString = new MyWebClient().DownloadString(url);
        ...
    }
}

class CallingClass
{
     public void CallingMethod()
     {
         ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true;
         //With or without the above line ^, the same TlsException is thrown. 
         GetHtml.Get("https://www.urbandictionary.com/define.php?term=example");
         //HTTP works properly, but HTTPS, as in this example, does not.
     }
}

日志如下：

TlsException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.RecordProtocol.ProcessAlert (AlertLevel alertLevel, AlertDescription alertDesc)
Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult)
Rethrow as IOException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult)
Rethrow as WebException: Error getting response stream (Write: The authentication or decryption has failed.): SendFailure
System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult)
System.Net.HttpWebRequest.GetResponse ()
System.Net.WebClient.GetWebResponse (System.Net.WebRequest request)
System.Net.WebClient.DownloadDataCore (System.Uri address, System.Object userToken)

编辑：我已经尝试更新运行时版本。唯一的选择是在Project Settings-> Player菜单中从.Net 3.5更改为4.6，这是实验性的。代码运行时我仍然会遇到异常，但输出日志略有不同。

TlsException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.RecordProtocol.EndReceiveRecord (System.IAsyncResult asyncResult) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Mono.Security.Protocol.Tls.SslClientStream.SafeEndReceiveRecord (System.IAsyncResult ar, System.Boolean ignoreEmpty) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Mono.Security.Protocol.Tls.SslClientStream.NegotiateAsyncWorker (System.IAsyncResult result) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Rethrow as IOException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.SslClientStream.EndNegotiateHandshake (System.IAsyncResult result) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (System.IAsyncResult asyncResult) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Rethrow as IOException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.SslStreamBase.EndRead (System.IAsyncResult asyncResult) (at <eb1224ae7b184cd09343d47f8a05481b>:0)
Mono.Net.Security.Private.LegacySslStream.EndAuthenticateAsClient (System.IAsyncResult asyncResult) (at <344dc4d3f1ad41809df78607b6121a41>:0)
Mono.Net.Security.Private.LegacySslStream.AuthenticateAsClient (System.String targetHost, System.Security.Cryptography.X509Certificates.X509CertificateCollection clientCertificates, System.Security.Authentication.SslProtocols enabledSslProtocols, System.Boolean checkCertificateRevocation) (at <344dc4d3f1ad41809df78607b6121a41>:0)
Mono.Net.Security.MonoTlsStream.CreateStream (System.Byte[] buffer) (at <344dc4d3f1ad41809df78607b6121a41>:0)
System.Net.WebConnection.CreateStream (System.Net.HttpWebRequest request) (at <344dc4d3f1ad41809df78607b6121a41>:0)
Rethrow as WebException: Error: SecureChannelFailure (The authentication or decryption has failed.)
System.Net.WebClient.DownloadDataInternal (System.Uri address, System.Net.WebRequest& request) (at <344dc4d3f1ad41809df78607b6121a41>:0)
System.Net.WebClient.DownloadString (System.Uri address) (at <344dc4d3f1ad41809df78607b6121a41>:0)
System.Net.WebClient.DownloadString (System.String address) (at <344dc4d3f1ad41809df78607b6121a41>:0)

Answer 1

另一答案