Add SNI support #2357

build/dependencies.props

@@ -7,39 +7,39 @@
     <BenchmarkDotNetPackageVersion>0.10.13</BenchmarkDotNetPackageVersion>
     <InternalAspNetCoreSdkPackageVersion>2.1.0-preview2-15749</InternalAspNetCoreSdkPackageVersion>
     <LibuvPackageVersion>1.10.0</LibuvPackageVersion>
-    <MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>2.1.0-a-preview2-mpr-16443</MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>
+    <MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreBenchmarkRunnerSourcesPackageVersion>
-    <MicrosoftAspNetCoreCertificatesGenerationSourcesPackageVersion>2.1.0-a-preview2-mpr-16443</MicrosoftAspNetCoreCertificatesGenerationSourcesPackageVersion>
+    <MicrosoftAspNetCoreCertificatesGenerationSourcesPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreCertificatesGenerationSourcesPackageVersion>
-    <MicrosoftAspNetCoreHostingAbstractionsPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreHostingAbstractionsPackageVersion>
+    <MicrosoftAspNetCoreHostingAbstractionsPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreHostingAbstractionsPackageVersion>
-    <MicrosoftAspNetCoreHostingPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreHostingPackageVersion>
+    <MicrosoftAspNetCoreHostingPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreHostingPackageVersion>
-    <MicrosoftAspNetCoreHttpAbstractionsPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreHttpAbstractionsPackageVersion>
+    <MicrosoftAspNetCoreHttpAbstractionsPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreHttpAbstractionsPackageVersion>
-    <MicrosoftAspNetCoreHttpFeaturesPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreHttpFeaturesPackageVersion>
+    <MicrosoftAspNetCoreHttpFeaturesPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreHttpFeaturesPackageVersion>
-    <MicrosoftAspNetCoreHttpPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreHttpPackageVersion>
+    <MicrosoftAspNetCoreHttpPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreHttpPackageVersion>
-    <MicrosoftAspNetCoreTestingPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreTestingPackageVersion>
+    <MicrosoftAspNetCoreTestingPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreTestingPackageVersion>
-    <MicrosoftAspNetCoreWebUtilitiesPackageVersion>2.1.0-preview2-30478</MicrosoftAspNetCoreWebUtilitiesPackageVersion>
+    <MicrosoftAspNetCoreWebUtilitiesPackageVersion>2.1.0-preview2-30554</MicrosoftAspNetCoreWebUtilitiesPackageVersion>
-    <MicrosoftExtensionsActivatorUtilitiesSourcesPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsActivatorUtilitiesSourcesPackageVersion>
+    <MicrosoftExtensionsActivatorUtilitiesSourcesPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsActivatorUtilitiesSourcesPackageVersion>
-    <MicrosoftExtensionsBuffersSourcesPackageVersion>2.1.0-a-preview2-mpr-16443</MicrosoftExtensionsBuffersSourcesPackageVersion>
+    <MicrosoftExtensionsBuffersSourcesPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsBuffersSourcesPackageVersion>
-    <MicrosoftExtensionsBuffersTestingSourcesPackageVersion>2.1.0-a-preview2-mpr-16443</MicrosoftExtensionsBuffersTestingSourcesPackageVersion>
+    <MicrosoftExtensionsBuffersTestingSourcesPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsBuffersTestingSourcesPackageVersion>
-    <MicrosoftExtensionsConfigurationBinderPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsConfigurationBinderPackageVersion>
+    <MicrosoftExtensionsConfigurationBinderPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsConfigurationBinderPackageVersion>
-    <MicrosoftExtensionsConfigurationJsonPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsConfigurationJsonPackageVersion>
+    <MicrosoftExtensionsConfigurationJsonPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsConfigurationJsonPackageVersion>
-    <MicrosoftExtensionsDependencyInjectionPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsDependencyInjectionPackageVersion>
+    <MicrosoftExtensionsDependencyInjectionPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsDependencyInjectionPackageVersion>
-    <MicrosoftExtensionsLoggingAbstractionsPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsLoggingAbstractionsPackageVersion>
+    <MicrosoftExtensionsLoggingAbstractionsPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsLoggingAbstractionsPackageVersion>
-    <MicrosoftExtensionsLoggingConsolePackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsLoggingConsolePackageVersion>
+    <MicrosoftExtensionsLoggingConsolePackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsLoggingConsolePackageVersion>
-    <MicrosoftExtensionsLoggingPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsLoggingPackageVersion>
+    <MicrosoftExtensionsLoggingPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsLoggingPackageVersion>
-    <MicrosoftExtensionsLoggingTestingPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsLoggingTestingPackageVersion>
+    <MicrosoftExtensionsLoggingTestingPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsLoggingTestingPackageVersion>
-    <MicrosoftExtensionsOptionsPackageVersion>2.1.0-preview2-30478</MicrosoftExtensionsOptionsPackageVersion>
+    <MicrosoftExtensionsOptionsPackageVersion>2.1.0-preview2-30554</MicrosoftExtensionsOptionsPackageVersion>
     <MicrosoftNETCoreApp20PackageVersion>2.0.0</MicrosoftNETCoreApp20PackageVersion>
-    <MicrosoftNETCoreApp21PackageVersion>2.1.0-preview3-26331-01</MicrosoftNETCoreApp21PackageVersion>
+    <MicrosoftNETCoreApp21PackageVersion>2.1.0-preview2-26403-06</MicrosoftNETCoreApp21PackageVersion>
-    <MicrosoftNetHttpHeadersPackageVersion>2.1.0-preview2-30478</MicrosoftNetHttpHeadersPackageVersion>
+    <MicrosoftNetHttpHeadersPackageVersion>2.1.0-preview2-30554</MicrosoftNetHttpHeadersPackageVersion>
     <MicrosoftNETTestSdkPackageVersion>15.6.1</MicrosoftNETTestSdkPackageVersion>
     <MoqPackageVersion>4.7.49</MoqPackageVersion>
     <NewtonsoftJsonPackageVersion>11.0.2</NewtonsoftJsonPackageVersion>
-    <SystemBuffersPackageVersion>4.5.0-preview3-26331-02</SystemBuffersPackageVersion>
+    <SystemBuffersPackageVersion>4.5.0-preview2-26403-05</SystemBuffersPackageVersion>
-    <SystemIOPipelinesPackageVersion>4.5.0-preview3-26331-02</SystemIOPipelinesPackageVersion>
+    <SystemIOPipelinesPackageVersion>4.5.0-preview2-26403-05</SystemIOPipelinesPackageVersion>
-    <SystemMemoryPackageVersion>4.5.0-preview3-26331-02</SystemMemoryPackageVersion>
+    <SystemMemoryPackageVersion>4.5.0-preview2-26403-05</SystemMemoryPackageVersion>
-    <SystemNumericsVectorsPackageVersion>4.5.0-preview3-26331-02</SystemNumericsVectorsPackageVersion>
+    <SystemNumericsVectorsPackageVersion>4.5.0-preview2-26403-05</SystemNumericsVectorsPackageVersion>
-    <SystemRuntimeCompilerServicesUnsafePackageVersion>4.5.0-preview3-26331-02</SystemRuntimeCompilerServicesUnsafePackageVersion>
+    <SystemRuntimeCompilerServicesUnsafePackageVersion>4.5.0-preview2-26403-05</SystemRuntimeCompilerServicesUnsafePackageVersion>
-    <SystemSecurityCryptographyCngPackageVersion>4.5.0-preview3-26331-02</SystemSecurityCryptographyCngPackageVersion>
+    <SystemSecurityCryptographyCngPackageVersion>4.5.0-preview2-26403-05</SystemSecurityCryptographyCngPackageVersion>
-    <SystemThreadingTasksExtensionsPackageVersion>4.5.0-preview3-26331-02</SystemThreadingTasksExtensionsPackageVersion>
+    <SystemThreadingTasksExtensionsPackageVersion>4.5.0-preview2-26403-05</SystemThreadingTasksExtensionsPackageVersion>
     <XunitAnalyzersPackageVersion>0.8.0</XunitAnalyzersPackageVersion>
     <XunitPackageVersion>2.3.1</XunitPackageVersion>
     <XunitRunnerVisualStudioPackageVersion>2.4.0-beta.1.build3945</XunitRunnerVisualStudioPackageVersion>

samples/SampleApp/Startup.cs

@@ -12,6 +12,7 @@ using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Server.Kestrel.Core;
+using Microsoft.AspNetCore.Server.Kestrel.Https.Internal;
 using Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions.Internal;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;
@@ -105,10 +106,23 @@ namespace SampleApp
                         listenOptions.UseHttps(StoreName.My, "localhost", allowInvalid: true);
                     });
 
+                    options.ListenAnyIP(basePort + 5, listenOptions =>
+                    {
+                        listenOptions.UseHttps(httpsOptions =>
+                        {
+                            var localhostCert = CertificateLoader.LoadFromStoreCert("localhost", "My", StoreLocation.CurrentUser, allowInvalid: true);
+                            httpsOptions.ServerCertificateSelector = (features, name) =>
+                            {
+                                // Here you would check the name, select an appropriate cert, and provide a fallback or fail for null names.
+                                return localhostCert;
+                            };
+                        });
+                    });
+
                     options
                         .Configure()
-                        .Endpoint(IPAddress.Loopback, basePort + 5)
+                        .Endpoint(IPAddress.Loopback, basePort + 6)
-                        .LocalhostEndpoint(basePort + 6)
+                        .LocalhostEndpoint(basePort + 7)
                         .Load();
 
                     options

src/Kestrel.Core/CoreStrings.resx

@@ -477,7 +477,7 @@
   <data name="PositiveTimeSpanRequired1" xml:space="preserve">
     <value>Value must be a positive TimeSpan.</value>
   </data>
-  <data name="ServiceCertificateRequired" xml:space="preserve">
+  <data name="ServerCertificateRequired" xml:space="preserve">
     <value>The server certificate parameter is required.</value>
   </data>
   <data name="BindingToDefaultAddresses" xml:space="preserve">

src/Kestrel.Core/HttpsConnectionAdapterOptions.cs

@@ -6,6 +6,7 @@ using System.Net.Security;
 using System.Security.Authentication;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
+using Microsoft.AspNetCore.Http.Features;
 using Microsoft.AspNetCore.Server.Kestrel.Core;
 
 namespace Microsoft.AspNetCore.Server.Kestrel.Https
@@ -29,7 +30,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https
 
         /// <summary>
         /// <para>
-        /// Specifies the server certificate used to authenticate HTTPS connections.
+        /// Specifies the server certificate used to authenticate HTTPS connections. This is ignored if ServerCertificateSelector is set.
         /// </para>
         /// <para>
         /// If the server certificate has an Extended Key Usage extension, the usages must include Server Authentication (OID 1.3.6.1.5.5.7.3.1).
@@ -37,6 +38,17 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https
         /// </summary>
         public X509Certificate2 ServerCertificate { get; set; }
 
+        /// <summary>
+        /// <para>
+        /// A callback that will be invoked to dynamically select a server certificate. This is higher priority than ServerCertificate.
+        /// If SNI is not avialable then the name parameter will be null.
+        /// </para>
+        /// <para>
+        /// If the server certificate has an Extended Key Usage extension, the usages must include Server Authentication (OID 1.3.6.1.5.5.7.3.1).
+        /// </para>
+        /// </summary>
+        public Func<IFeatureCollection, string, X509Certificate2> ServerCertificateSelector { get; set; }
+
         /// <summary>
         /// Specifies the client certificate requirements for a HTTPS connection. Defaults to <see cref="ClientCertificateMode.NoCertificate"/>.
         /// </summary>

src/Kestrel.Core/Internal/HttpsConnectionAdapter.cs

@@ -22,6 +22,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https.Internal
 
         private readonly HttpsConnectionAdapterOptions _options;
         private readonly X509Certificate2 _serverCertificate;
+        private readonly Func<IFeatureCollection, string, X509Certificate2> _serverCertificateSelector;
+
         private readonly ILogger _logger;
 
         public HttpsConnectionAdapter(HttpsConnectionAdapterOptions options)
@@ -36,15 +38,24 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https.Internal
                 throw new ArgumentNullException(nameof(options));
             }
 
-            if (options.ServerCertificate == null)
+            // capture the certificate now so it can't be switched after validation
+            _serverCertificate = options.ServerCertificate;
+            _serverCertificateSelector = options.ServerCertificateSelector;
+            if (_serverCertificate == null && _serverCertificateSelector == null)
             {
-                throw new ArgumentException(CoreStrings.ServiceCertificateRequired, nameof(options));
+                throw new ArgumentException(CoreStrings.ServerCertificateRequired, nameof(options));
             }
 
-            // capture the certificate now so it can be switched after validation
+            // If a selector is provided then ignore the cert, it may be a default cert.
-            _serverCertificate = options.ServerCertificate;
+            if (_serverCertificateSelector != null)
-
+            {
-            EnsureCertificateIsAllowedForServerAuth(_serverCertificate);
+                // SslStream doesn't allow both.
+                _serverCertificate = null;
+            }
+            else
+            {
+                EnsureCertificateIsAllowedForServerAuth(_serverCertificate);
+            }
 
             _options = options;
             _logger = loggerFactory?.CreateLogger(nameof(HttpsConnectionAdapter));
@@ -115,9 +126,26 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https.Internal
             try
             {
 #if NETCOREAPP2_1
+                // Adapt to the SslStream signature
+                ServerCertificateSelectionCallback selector = null;
+                if (_serverCertificateSelector != null)
+                {
+                    selector = (sender, name) =>
+                    {
+                        context.Features.Set(sslStream);
+                        var cert = _serverCertificateSelector(context.Features, name);
+                        if (cert != null)
+                        {
+                            EnsureCertificateIsAllowedForServerAuth(cert);
+                        }
+                        return cert;
+                    };
+                }
+
                 var sslOptions = new SslServerAuthenticationOptions()
                 {
                     ServerCertificate = _serverCertificate,
+                    ServerCertificateSelectionCallback = selector,
                     ClientCertificateRequired = certificateRequired,
                     EnabledSslProtocols = _options.SslProtocols,
                     CertificateRevocationCheckMode = _options.CheckCertificateRevocation ? X509RevocationMode.Online : X509RevocationMode.NoCheck,
@@ -137,7 +165,17 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Https.Internal
 
                 await sslStream.AuthenticateAsServerAsync(sslOptions, CancellationToken.None);
 #else
-                await sslStream.AuthenticateAsServerAsync(_serverCertificate, certificateRequired,
+                var serverCert = _serverCertificate;
+                if (_serverCertificateSelector != null)
+                {
+                    context.Features.Set(sslStream);
+                    serverCert = _serverCertificateSelector(context.Features, null);                
+                    if (serverCert != null)
+                    {
+                        EnsureCertificateIsAllowedForServerAuth(serverCert);
+                    }
+                }
+                await sslStream.AuthenticateAsServerAsync(serverCert, certificateRequired,
                         _options.SslProtocols, _options.CheckCertificateRevocation);
 #endif
             }

src/Kestrel.Core/KestrelConfigurationLoader.cs

@@ -236,7 +236,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel
                 // EndpointDefaults or configureEndpoint may have added an https adapter.
                 if (https && !listenOptions.ConnectionAdapters.Any(f => f.IsHttps))
                 {
-                    if (httpsOptions.ServerCertificate == null)
+                    if (httpsOptions.ServerCertificate == null && httpsOptions.ServerCertificateSelector == null)
                     {
                         throw new InvalidOperationException(CoreStrings.NoCertSpecifiedNoDevelopmentCertificateFound);
                     }

src/Kestrel.Core/ListenOptionsHttpsExtensions.cs

@@ -179,7 +179,7 @@ namespace Microsoft.AspNetCore.Hosting
             listenOptions.KestrelServerOptions.ApplyHttpsDefaults(options);
             configureOptions(options);
 
-            if (options.ServerCertificate == null)
+            if (options.ServerCertificate == null && options.ServerCertificateSelector == null)
             {
                 throw new InvalidOperationException(CoreStrings.NoCertSpecifiedNoDevelopmentCertificateFound);
             }
@@ -192,7 +192,7 @@ namespace Microsoft.AspNetCore.Hosting
             var options = new HttpsConnectionAdapterOptions();
             listenOptions.KestrelServerOptions.ApplyHttpsDefaults(options);
 
-            if (options.ServerCertificate == null)
+            if (options.ServerCertificate == null && options.ServerCertificateSelector == null)
             {
                 return false;
             }

src/Kestrel.Core/Properties/CoreStrings.Designer.cs

@@ -1693,16 +1693,16 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core
         /// <summary>
         /// The server certificate parameter is required.
         /// </summary>
-        internal static string ServiceCertificateRequired
+        internal static string ServerCertificateRequired
         {
-            get => GetString("ServiceCertificateRequired");
+            get => GetString("ServerCertificateRequired");
         }
 
         /// <summary>
         /// The server certificate parameter is required.
         /// </summary>
-        internal static string FormatServiceCertificateRequired()
+        internal static string FormatServerCertificateRequired()
-            => GetString("ServiceCertificateRequired");
+            => GetString("ServerCertificateRequired");
 
         /// <summary>
         /// No listening endpoints were configured. Binding to {address0} and {address1} by default.

test/Kestrel.FunctionalTests/HttpsConnectionAdapterTests.cs

@@ -26,7 +26,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
 {
     public class HttpsConnectionAdapterTests
     {
-        private static X509Certificate2 _x509Certificate2 = new X509Certificate2(TestResources.TestCertificatePath, "testPassword");
+        private static X509Certificate2 _x509Certificate2 = TestResources.GetTestCertificate();
+        private static X509Certificate2 _x509Certificate2NoExt = TestResources.GetTestCertificate("no_extensions.pfx");
         private readonly ITestOutputHelper _output;
 
         public HttpsConnectionAdapterTests(ITestOutputHelper output)
@@ -148,6 +149,211 @@ namespace Microsoft.AspNetCore.Server.Kestrel.FunctionalTests
             }
         }
 
+        [Fact]
+        public async Task UsesProvidedServerCertificateSelector()
+        {
+            var selectorCalled = 0;
+            var serviceContext = new TestServiceContext();
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters =
+                {
+                    new HttpsConnectionAdapter(new HttpsConnectionAdapterOptions
+                    {
+                        ServerCertificateSelector = (features, name) =>
+                        {
+                            Assert.NotNull(features);
+                            Assert.NotNull(features.Get<SslStream>());
+#if NETCOREAPP2_1
+                            Assert.Equal("localhost", name);
+#else
+                            Assert.Null(name);
+#endif
+                            selectorCalled++;
+                            return _x509Certificate2;
+                        }
+                    })
+                }
+            };
+            using (var server = new TestServer(context => Task.CompletedTask, serviceContext, listenOptions))
+            {
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false);
+                    Assert.True(stream.RemoteCertificate.Equals(_x509Certificate2));
+                    Assert.Equal(1, selectorCalled);
+                }
+            }
+        }
+
+        [Fact]
+        public async Task UsesProvidedServerCertificateSelectorEachTime()
+        {
+            var selectorCalled = 0;
+            var serviceContext = new TestServiceContext();
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters =
+                {
+                    new HttpsConnectionAdapter(new HttpsConnectionAdapterOptions
+                    {
+                        ServerCertificateSelector = (features, name) =>
+                        {
+                            Assert.NotNull(features);
+                            Assert.NotNull(features.Get<SslStream>());
+#if NETCOREAPP2_1
+                            Assert.Equal("localhost", name);
+#else
+                            Assert.Null(name);
+#endif
+                            selectorCalled++;
+                            if (selectorCalled == 1)
+                            {
+                                return _x509Certificate2;
+                            }
+                            return _x509Certificate2NoExt;
+                        }
+                    })
+                }
+            };
+            using (var server = new TestServer(context => Task.CompletedTask, serviceContext, listenOptions))
+            {
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false);
+                    Assert.True(stream.RemoteCertificate.Equals(_x509Certificate2));
+                    Assert.Equal(1, selectorCalled);
+                }
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false);
+                    Assert.True(stream.RemoteCertificate.Equals(_x509Certificate2NoExt));
+                    Assert.Equal(2, selectorCalled);
+                }
+            }
+        }
+
+        [Fact]
+        public async Task UsesProvidedServerCertificateSelectorValidatesEkus()
+        {
+            var selectorCalled = 0;
+            var serviceContext = new TestServiceContext();
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters =
+                {
+                    new HttpsConnectionAdapter(new HttpsConnectionAdapterOptions
+                    {
+                        ServerCertificateSelector = (features, name) =>
+                        {
+                            selectorCalled++;
+                            return TestResources.GetTestCertificate("eku.code_signing.pfx");
+                        }
+                    })
+                }
+            };
+            using (var server = new TestServer(context => Task.CompletedTask, serviceContext, listenOptions))
+            {
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await Assert.ThrowsAsync<IOException>(() =>
+                        stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false));
+                    Assert.Equal(1, selectorCalled);
+                }
+            }
+        }
+
+        [Fact]
+        public async Task UsesProvidedServerCertificateSelectorOverridesServerCertificate()
+        {
+            var selectorCalled = 0;
+            var serviceContext = new TestServiceContext();
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters =
+                {
+                    new HttpsConnectionAdapter(new HttpsConnectionAdapterOptions
+                    {
+                        ServerCertificate = _x509Certificate2NoExt,
+                        ServerCertificateSelector = (features, name) =>
+                        {
+                            Assert.NotNull(features);
+                            Assert.NotNull(features.Get<SslStream>());
+#if NETCOREAPP2_1
+                            Assert.Equal("localhost", name);
+#else
+                            Assert.Null(name);
+#endif
+                            selectorCalled++;
+                            return _x509Certificate2;
+                        }
+                    })
+                }
+            };
+            using (var server = new TestServer(context => Task.CompletedTask, serviceContext, listenOptions))
+            {
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false);
+                    Assert.True(stream.RemoteCertificate.Equals(_x509Certificate2));
+                    Assert.Equal(1, selectorCalled);
+                }
+            }
+        }
+
+        [Fact]
+        public async Task UsesProvidedServerCertificateSelectorFailsIfYouReturnNull()
+        {
+            var selectorCalled = 0;
+            var serviceContext = new TestServiceContext();
+            var listenOptions = new ListenOptions(new IPEndPoint(IPAddress.Loopback, 0))
+            {
+                ConnectionAdapters =
+                {
+                    new HttpsConnectionAdapter(new HttpsConnectionAdapterOptions
+                    {
+                        ServerCertificateSelector = (features, name) =>
+                        {
+                            selectorCalled++;
+                            return null;
+                        }
+                    })
+                }
+            };
+            using (var server = new TestServer(context => Task.CompletedTask, serviceContext, listenOptions))
+            {
+                using (var client = new TcpClient())
+                {
+                    // SslStream is used to ensure the certificate is actually passed to the server
+                    // HttpClient might not send the certificate because it is invalid or it doesn't match any
+                    // of the certificate authorities sent by the server in the SSL handshake.
+                    var stream = await OpenSslStream(client, server);
+                    await Assert.ThrowsAsync<IOException>(() =>
+                        stream.AuthenticateAsClientAsync("localhost", new X509CertificateCollection(), SslProtocols.Tls12 | SslProtocols.Tls11, false));
+                    Assert.Equal(1, selectorCalled);
+                }
+            }
+        }
 
         [Fact]
         public async Task CertificatePassedToHttpContext()

test/shared/TestResources.cs

@@ -17,5 +17,10 @@ namespace Microsoft.AspNetCore.Testing
         {
             return new X509Certificate2(TestCertificatePath, "testPassword");
         }
+
+        public static X509Certificate2 GetTestCertificate(string certName)
+        {
+            return new X509Certificate2(GetCertPath(certName), "testPassword");
+        }
     }
 }