[Platform] Provide a better error message when the developer certificate can't be used

src/Servers/Kestrel/Core/src/CoreStrings.resx

@@ -617,4 +617,7 @@ For more information on configuring HTTPS see https://go.microsoft.com/fwlink/?l
   <data name="Http2TellClientToCalmDown" xml:space="preserve">
     <value>A new stream was refused because this connection has too many streams that haven't finished processing. This may happen if many streams are aborted but not yet cleaned up.</value>
   </data>
+  <data name="BadDeveloperCertificateState" xml:space="preserve">
+    <value>The ASP.NET Core developer certificate is in an invalid state. To fix this issue, run the following commands 'dotnet dev-certs https --clean' and 'dotnet dev-certs https' to remove all existing ASP.NET Core development certificates and create a new untrusted developer certificate. On macOS or Windows, use 'dotnet dev-certs https --trust' to trust the new certificate.</value>
+  </data>
 </root>

src/Servers/Kestrel/Core/src/KestrelServerOptions.cs

@@ -142,8 +142,7 @@ private void EnsureDefaultCert()
                 var logger = ApplicationServices.GetRequiredService<ILogger<KestrelServer>>();
                 try
                 {
-                    var certificateManager = new CertificateManager();
-                    DefaultCertificate = certificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true)
+                    DefaultCertificate = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true)
                         .FirstOrDefault();
 
                     if (DefaultCertificate != null)

src/Servers/Kestrel/Core/src/Middleware/HttpsConnectionMiddleware.cs

@@ -11,6 +11,7 @@
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Certificates.Generation;
 using Microsoft.AspNetCore.Connections;
 using Microsoft.AspNetCore.Connections.Features;
 using Microsoft.AspNetCore.Http.Features;
@@ -208,12 +209,28 @@ private async Task InnerOnConnectionAsync(ConnectionContext context)
                     await sslStream.DisposeAsync();
                     return;
                 }
-                catch (Exception ex) when (ex is IOException || ex is AuthenticationException)
+                catch (IOException ex)
                 {
                     _logger?.LogDebug(1, ex, CoreStrings.AuthenticationFailed);
                     await sslStream.DisposeAsync();
                     return;
                 }
+                catch (AuthenticationException ex)
+                {
+                    if (_serverCertificate == null ||
+                        !CertificateManager.IsHttpsDevelopmentCertificate(_serverCertificate) ||
+                        CertificateManager.CheckDeveloperCertificateKey(_serverCertificate))
+                    {
+                        _logger?.LogDebug(1, ex, CoreStrings.AuthenticationFailed);
+                    }
+                    else
+                    {
+                        _logger?.LogError(2, ex, CoreStrings.BadDeveloperCertificateState);
+                    }
+
+                    await sslStream.DisposeAsync();
+                    return;
+                }
             }
 
             feature.ApplicationProtocol = sslStream.NegotiatedApplicationProtocol.Protocol;

src/Servers/Kestrel/test/InMemory.FunctionalTests/HttpsTests.cs

@@ -364,7 +364,7 @@ public async Task ClientAttemptingToUseUnsupportedProtocolIsLoggedAsDebug()
                 new TestServiceContext(LoggerFactory),
                 listenOptions =>
                 {
-                    listenOptions.UseHttps(TestResources.GetTestCertificate());
+                    listenOptions.UseHttps(TestResources.GetTestCertificate("no_extensions.pfx"));
                 }))
             {
                 using (var connection = server.CreateConnection())
@@ -383,6 +383,35 @@ await Assert.ThrowsAsync<IOException>(() =>
             Assert.Equal(LogLevel.Debug, loggerProvider.FilterLogger.LastLogLevel);
         }
 
+        [Fact]
+        public async Task DevCertWithInvalidPrivateKeyProducesCustomWarning()
+        {
+            var loggerProvider = new HandshakeErrorLoggerProvider();
+            LoggerFactory.AddProvider(loggerProvider);
+
+            await using (var server = new TestServer(context => Task.CompletedTask,
+                new TestServiceContext(LoggerFactory),
+                listenOptions =>
+                {
+                    listenOptions.UseHttps(TestResources.GetTestCertificate());
+                }))
+            {
+                using (var connection = server.CreateConnection())
+                using (var sslStream = new SslStream(connection.Stream, true, (sender, certificate, chain, errors) => true))
+                {
+                    // SslProtocols.Tls is TLS 1.0 which isn't supported by Kestrel by default.
+                    await Assert.ThrowsAsync<IOException>(() =>
+                        sslStream.AuthenticateAsClientAsync("127.0.0.1", clientCertificates: null,
+                            enabledSslProtocols: SslProtocols.Tls,
+                            checkCertificateRevocation: false));
+                }
+            }
+
+            await loggerProvider.FilterLogger.LogTcs.Task.DefaultTimeout();
+            Assert.Equal(2, loggerProvider.FilterLogger.LastEventId);
+            Assert.Equal(LogLevel.Error, loggerProvider.FilterLogger.LastLogLevel);
+        }
+
         [Fact]
         public async Task OnAuthenticate_SeesOtherSettings()
         {

src/Shared/CertificateGeneration/CertificateManager.cs

@@ -44,9 +44,13 @@ internal class CertificateManager
 
         // Setting to 0 means we don't append the version byte,
         // which is what all machines currently have.
-        public int AspNetHttpsCertificateVersion { get; set; } = 1;
+        public static int AspNetHttpsCertificateVersion { get; set; } = 1;
 
-        public IList<X509Certificate2> ListCertificates(
+        public static bool IsHttpsDevelopmentCertificate(X509Certificate2 certificate) =>
+            certificate.Extensions.OfType<X509Extension>()
+            .Any(e => string.Equals(AspNetHttpsOid, e.Oid.Value, StringComparison.Ordinal));
+
+        public static IList<X509Certificate2> ListCertificates(
             CertificatePurpose purpose,
             StoreName storeName,
             StoreLocation location,
@@ -228,6 +232,33 @@ public X509Certificate2 CreateAspNetCoreHttpsDevelopmentCertificate(DateTimeOffs
             return certificate;
         }
 
+        internal static bool CheckDeveloperCertificateKey(X509Certificate2 candidate)
+        {
+            // Tries to use the certificate key to validate it can't access it
+            try
+            {
+                var rsa = candidate.GetRSAPrivateKey();
+                if (rsa == null)
+                {
+                    return false;
+                }
+
+                // Encrypting a random value is the ultimate test for a key validity.
+                // Windows and Mac OS both return HasPrivateKey = true if there is (or there has been) a private key associated
+                // with the certificate at some point.
+                var value = new byte[32];
+                RandomNumberGenerator.Fill(value);
+                rsa.Decrypt(rsa.Encrypt(value, RSAEncryptionPadding.Pkcs1), RSAEncryptionPadding.Pkcs1);
+
+                // Being able to encrypt and decrypt a payload is the strongest guarantee that the key is valid.
+                return true;
+            }
+            catch (Exception)
+            {
+                return false;
+            }
+        }
+
         public X509Certificate2 CreateSelfSignedCertificate(
             X500DistinguishedName subject,
             IEnumerable<X509Extension> extensions,

src/Tools/FirstRunCertGenerator/test/CertificateManagerTests.cs

@@ -52,7 +52,7 @@ public void EnsureCreateHttpsCertificate_CreatesACertificate_WhenThereAreNoHttps
                 Assert.NotNull(exportedCertificate);
                 Assert.False(exportedCertificate.HasPrivateKey);
 
-                var httpsCertificates = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false);
+                var httpsCertificates = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false);
                 var httpsCertificate = Assert.Single(httpsCertificates, c => c.Subject == TestCertificateSubject);
                 Assert.True(httpsCertificate.HasPrivateKey);
                 Assert.Equal(TestCertificateSubject, httpsCertificate.Subject);
@@ -94,7 +94,7 @@ public void EnsureCreateHttpsCertificate_CreatesACertificate_WhenThereAreNoHttps
                     httpsCertificate.Extensions.OfType<X509Extension>(),
                     e => e.Critical == false &&
                         e.Oid.Value == "1.3.6.1.4.1.311.84.1.1" &&
-                        e.RawData[0] == _manager.AspNetHttpsCertificateVersion);
+                        e.RawData[0] == CertificateManager.AspNetHttpsCertificateVersion);
 
                 Assert.Equal(httpsCertificate.GetCertHashString(), exportedCertificate.GetCertHashString());
 
@@ -137,7 +137,7 @@ public void EnsureCreateHttpsCertificate_DoesNotCreateACertificate_WhenThereIsAn
             now = new DateTimeOffset(now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second, 0, now.Offset);
             _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), path: null, trust: false, subject: TestCertificateSubject);
 
-            var httpsCertificate = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false).Single(c => c.Subject == TestCertificateSubject);
+            var httpsCertificate = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false).Single(c => c.Subject == TestCertificateSubject);
 
             // Act
             var result = _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), CertificateName, trust: false, includePrivateKey: true, password: certificatePassword, subject: TestCertificateSubject);
@@ -164,9 +164,9 @@ public void EnsureCreateHttpsCertificate_ReturnsExpiredCertificateIfVersionIsInc
             now = new DateTimeOffset(now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second, 0, now.Offset);
             _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), path: null, trust: false, subject: TestCertificateSubject);
 
-            _manager.AspNetHttpsCertificateVersion = 2;
+            CertificateManager.AspNetHttpsCertificateVersion = 2;
 
-            var httpsCertificateList = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
+            var httpsCertificateList = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
             Assert.Empty(httpsCertificateList);
         }
 
@@ -178,12 +178,12 @@ public void EnsureCreateHttpsCertificate_ReturnsExpiredCertificateForEmptyVersio
 
             DateTimeOffset now = DateTimeOffset.UtcNow;
             now = new DateTimeOffset(now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second, 0, now.Offset);
-            _manager.AspNetHttpsCertificateVersion = 0;
+            CertificateManager.AspNetHttpsCertificateVersion = 0;
             _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), path: null, trust: false, subject: TestCertificateSubject);
 
-            _manager.AspNetHttpsCertificateVersion = 1;
+            CertificateManager.AspNetHttpsCertificateVersion = 1;
 
-            var httpsCertificateList = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
+            var httpsCertificateList = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
             Assert.Empty(httpsCertificateList);
         }
 
@@ -195,10 +195,10 @@ public void EnsureCreateHttpsCertificate_ReturnsValidIfVersionIsZero()
 
             DateTimeOffset now = DateTimeOffset.UtcNow;
             now = new DateTimeOffset(now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second, 0, now.Offset);
-            _manager.AspNetHttpsCertificateVersion = 0;
+            CertificateManager.AspNetHttpsCertificateVersion = 0;
             _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), path: null, trust: false, subject: TestCertificateSubject);
 
-            var httpsCertificateList = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
+            var httpsCertificateList = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
             Assert.NotEmpty(httpsCertificateList);
         }
 
@@ -210,11 +210,11 @@ public void EnsureCreateHttpsCertificate_ReturnValidIfCertIsNewer()
 
             DateTimeOffset now = DateTimeOffset.UtcNow;
             now = new DateTimeOffset(now.Year, now.Month, now.Day, now.Hour, now.Minute, now.Second, 0, now.Offset);
-            _manager.AspNetHttpsCertificateVersion = 2;
+            CertificateManager.AspNetHttpsCertificateVersion = 2;
             _manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), path: null, trust: false, subject: TestCertificateSubject);
 
-            _manager.AspNetHttpsCertificateVersion = 1;
-            var httpsCertificateList = _manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
+            CertificateManager.AspNetHttpsCertificateVersion = 1;
+            var httpsCertificateList = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
             Assert.NotEmpty(httpsCertificateList);
         }
 
@@ -241,10 +241,10 @@ public void EnsureAspNetCoreHttpsDevelopmentCertificate_CanRemoveCertificates()
 
             _manager.CleanupHttpsCertificates(TestCertificateSubject);
 
-            Assert.Empty(_manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false).Where(c => c.Subject == TestCertificateSubject));
+            Assert.Empty(CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: false).Where(c => c.Subject == TestCertificateSubject));
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
-                Assert.Empty(_manager.ListCertificates(CertificatePurpose.HTTPS, StoreName.Root, StoreLocation.CurrentUser, isValid: false).Where(c => c.Subject == TestCertificateSubject));
+                Assert.Empty(CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.Root, StoreLocation.CurrentUser, isValid: false).Where(c => c.Subject == TestCertificateSubject));
             }
         }
     }

src/Tools/dotnet-dev-certs/src/Program.cs

@@ -150,7 +150,7 @@ private static int CheckHttpsCertificate(CommandOption trust, IReporter reporter
         {
             var now = DateTimeOffset.Now;
             var certificateManager = new CertificateManager();
-            var certificates = certificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
+            var certificates = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, StoreName.My, StoreLocation.CurrentUser, isValid: true);
             if (certificates.Count == 0)
             {
                 reporter.Output("No valid certificate found.");
@@ -164,7 +164,7 @@ private static int CheckHttpsCertificate(CommandOption trust, IReporter reporter
             if (trust != null && trust.HasValue())
             {
                 var store = RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? StoreName.My : StoreName.Root;
-                var trustedCertificates = certificateManager.ListCertificates(CertificatePurpose.HTTPS, store, StoreLocation.CurrentUser, isValid: true);
+                var trustedCertificates = CertificateManager.ListCertificates(CertificatePurpose.HTTPS, store, StoreLocation.CurrentUser, isValid: true);
                 if (!certificates.Any(c => certificateManager.IsTrusted(c)))
                 {
                     reporter.Output($@"The following certificates were found, but none of them is trusted: