.net core中Grpc使用報錯：The remote certificate is invalid according to the validation procedure.

因為Grpc採用HTTP/2作為通信協議，預設採用LTS/SSL加密方式傳輸，比如使用.net core啟動一個服務端（被調用方）時：　　

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.ConfigureKestrel(options =>
                {
                    options.ListenAnyIP(5000, listenOptions =>
                    {
                        listenOptions.Protocols = HttpProtocols.Http2;
                        listenOptions.UseHttps("xxxxx.pfx", "password");
                    });
                });
                webBuilder.UseStartup<Startup>();
            });

　　其中使用UseHttps方法添加證書和秘鑰。

　　但是，有時候，比如開發階段，我們可能沒有證書，或者是一個自己製作的臨時測試證書，那麼在客戶端（調用方）調用是可能就會出現下麵的異常：　　

　　Call failed with gRPC error status. Status code: 'Internal', Message: 'Error starting gRPC call. HttpRequestException: The SSL connection could not be established, see inner exception. AuthenticationException: The remote certificate is invalid according to the validation procedure.'.
　　fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
   An unhandled exception has occurred while executing the request.
　　Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: The SSL connection could not be established, see inner exception. AuthenticationException: The remote certificate is invalid according to the validation procedure.", DebugException="System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception.
　　---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.
   at System.Net.Security.SslStream.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, ExceptionDispatchInfo exception)
   at System.Net.Security.SslStream.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslStream.PartialFrameCallback(AsyncProtocolRequest asyncRequest)
    --- End of stack trace from previous location where exception was thrown ---
   at System.Net.Security.SslStream.ThrowIfExceptional()
   at System.Net.Security.SslStream.InternalEndProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Net.Security.SslStream.EndProcessAuthentication(IAsyncResult result)
   at System.Net.Security.SslStream.EndAuthenticateAsClient(IAsyncResult asyncResult)
　　..........

 　　然而我們可能沒有辦法得到有效的證書，這時，我們有兩個辦法：

　　1、使用http協議

　　想想，我們為什麼要使用Grpc？因為高性能，高效率，簡單易用吧，但是https相比http就是多個加密的過程，這可能會有一定的性能損失（一般可忽略）。

　　而一般的，我們在微服務架構中使用Grpc比較多，而微服務一般部署在我們自己的一個子網下，這也就沒必要使用https了吧？

　    首先我們知道，Grpc是基於HTTP/2作為通信協議的，而HTTP/2預設是基於LTS/SSL加密技術的，或者說預設需要https協議支持（https=http+lts/ssl），而HTTP/2又支持明文傳輸，即對http也是支持，但是一般需要我們自己去設置。

　　當我們使用Grpc時，又不去改變這個預設行為，那可能就會導致上面的報錯。

　　在.net core開發中，Grpc要支持http，我們需要顯示的指定不需要TLS支持，官方給出的做法是添加如下配置（比如客戶端（調用方）在ConfigureServices添加）：　　

    public void ConfigureServices(IServiceCollection services)
    {
        //顯式的指定HTTP/2不需要TLS支持
        AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2UnencryptedSupport", true); 
        AppContext.SetSwitch("System.Net.Http.SocketsHttpHandler.Http2Support", true);

        services.AddGrpcClient<Greeter.GreeterClient>(nameof(Greeter.GreeterClient), options =>
        {
            options.Address = new Uri("http://localhost:5000");
        });

        ...
    }

　　2、調用時不對證書進行驗證

　　如果是控制台程式，我們可以這麼做：　　

    public static void Main(string[] args)
    {
        var channel = GrpcChannel.ForAddress("https://localhost:5000", new GrpcChannelOptions()
        {
            HttpClient = null,
            HttpHandler = new HttpClientHandler
            {
                //方法一
                ServerCertificateCustomValidationCallback = HttpClientHandler.DangerousAcceptAnyServerCertificateValidator
                //方法二
                //ServerCertificateCustomValidationCallback = (a, b, c, d) => true
            }
        });

        var client = new Greeter.GreeterClient(channel);
        var result = client.SayHello(new HelloRequest() { Name = "Grpc" });
    }

　　其中 HttpClientHandler 的 ServerCertificateCustomValidationCallback 是對證書的自定義驗證，上面給出了兩種方式驗證。

　　如果是.net core的webmvc或者webapi程式，因為.net core 3.x開始已經支持了Grpc的引入，所以我只需要在ConfigureServices中註入Grpc的客戶端是進行設置：　　

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddGrpcClient<Greeter.GreeterClient>(nameof(Greeter.GreeterClient), options =>
        {
            options.Address = new Uri("https://localhost:5000");
        }).ConfigurePrimaryHttpMessageHandler(() =>
        {
            return new HttpClientHandler
            {
                //方法一
                ServerCertificateCustomValidationCallback = HttpClientHandler.DangerousAcceptAnyServerCertificateValidator
                //方法二
                //ServerCertificateCustomValidationCallback = (a, b, c, d) => true
            };
        });

        ...
    }

　　因為.net core3.x中Grpc的使用是基於它的HttpClient機制，比如 AddGrpcClient 方法返回的就是一個 IHttpClientBuilder 介面對象，上面的配置我們還可以這麼寫：　　

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddGrpcClient<Greeter.GreeterClient>(nameof(Greeter.GreeterClient));
        services.AddHttpClient(nameof(Greeter.GreeterClient), httpClient =>
        {
            httpClient.BaseAddress = new Uri("https://localhost:5000");
        }).ConfigurePrimaryHttpMessageHandler(() =>
        {
            return new HttpClientHandler
            {
                //方法一
                ServerCertificateCustomValidationCallback = HttpClientHandler.DangerousAcceptAnyServerCertificateValidator
                //方法二
                //ServerCertificateCustomValidationCallback = (a, b, c, d) => true
            };
        });

        ...
    }

　　總之，不管怎麼調用，機制都是一樣的，最終都是像上面的客戶端調用一樣去創建Client，只要能理解就好了。