Xamarin Android问题通过HTTPS连接到具有自签名证书的站点：“找不到证书路径的信任锚”。

Question

我正在尝试对具有2个SSL证书的站点进行HTTPS调用：自签名证书和由第一个证书签名的证书。当我使用HttpClient向站点发送请求时，控制台会记录一个不受信任的链，显示两个证书，然后打印由java.security.cert.CertPathValidatorException: Trust anchor for certification path not found引起的长堆栈跟踪。

我已经在手机上安装了两个证书，导航Chrome到该站点显示了一个可信连接（在我安装证书之前它有一个不受信任的连接警告）。我认为问题在于App拒绝信任自签名证书。我无权访问服务器，因此对其证书没有影响，因此安装由可信CA签名的证书是不可行的。

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Solutions I've tried that have not worked.

ServicePointManager.ServerCertificateValidationCallback似乎没有运行。

我已经尝试将自己的函数用于ServicePointManager.ServerCertificateValidationCallback，但我给它的委托似乎永远不会运行。我在MainActivity.OnCreate方法中有以下代码，但控制台从不记录消息：

System.Net.ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) =>
{
  Console.WriteLine($"****************************************************************************************************");

  return true;
};

HttpClientHandler.ServerCertificateCustomValidationCallback抛出异常。

我已经尝试使用HttpClientHandler并设置其ServerCertificateCustomValidationCallback，但我只是得到消息：

System.NotImplementedException: The method or operation is not implemented. at System.Net.Http.HttpClientHandler.set_ServerCertificateCustomValidationCallback (System.Func`5[T1,T2,T3,T4,TResult] value)。

设置代码：

HttpClientHandler handler = new HttpClientHandler();
handler.ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true;
HttpClient client = new HttpClient(handler);

Answer 1

我能够在Android和iOS上都能使用它。

iOS很简单，只需覆盖ServicePointManager.ServerCertificateValidationCallback：

ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;

对于Android，我使用了Bruno Caceiro's answer from a similar question和创建的依赖服务。

在我的Xamarin Forms项目中，我添加了一个简单的界面：

public interface IHTTPClientHandlerCreationService
{
  HttpClientHandler GetInsecureHandler();
}

在我的Xamarin Android项目中，我实现了界面：

[assembly: Dependency(typeof(HTTPClientHandlerCreationService_Android))]
namespace MyApp.Droid
{
  public class HTTPClientHandlerCreationService_Android : CollateralUploader.Services.IHTTPClientHandlerCreationService
  {
    public HttpClientHandler GetInsecureHandler()
    {
      return new IgnoreSSLClientHandler();
    }
  }

  internal class IgnoreSSLClientHandler : AndroidClientHandler
  {
    protected override SSLSocketFactory ConfigureCustomSSLSocketFactory(HttpsURLConnection connection)
    {
      return SSLCertificateSocketFactory.GetInsecure(1000, null);
    }

    protected override IHostnameVerifier GetSSLHostnameVerifier(HttpsURLConnection connection)
    {
      return new IgnoreSSLHostnameVerifier();
    }
  }

  internal class IgnoreSSLHostnameVerifier : Java.Lang.Object, IHostnameVerifier
  {
    public bool Verify(string hostname, ISSLSession session)
    {
      return true;
    }
  }
}

用于正确设置HttpClient的共享代码：

switch (Device.RuntimePlatform)
{
  case Device.Android:
    this.httpClient = new HttpClient(DependencyService.Get<Services.IHTTPClientHandlerCreationService>().GetInsecureHandler());
    break;
  default:
    ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;
    this.httpClient = new HttpClient(new HttpClientHandler());
    break;
}