Moved the usage of certificate provider into the server listener (#1652)

* Moved the usage of certificate provider into the server listener so that each connection has the posibility of receiving a new SSL cert.

* Removed warning from unused field.

* Reduced changeds on original codebase.

---------

Co-authored-by: Jeff Scherrer <Jeff.Scherrer@vw.com>

Source/MQTTnet.Tests/Server/Tls_Tests.cs

@@ -0,0 +1,198 @@
+
+#if !WINDOWS_UWP && (NET48_OR_GREATER || NET5_0_OR_GREATER)
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using MQTTnet.Certificates;
+using MQTTnet.Client;
+using MQTTnet.Server;
+using MQTTnet.Tests.Mockups;
+using System;
+using System.Linq;
+using System.Net;
+using System.Security.Authentication;
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace MQTTnet.Tests.Server
+{
+
+    [TestClass]
+    
+    public class Tls_Tests : BaseTestClass
+    {
+
+        public X509Certificate2 CreateCertificate(string oid)
+        {
+            var sanBuilder = new SubjectAlternativeNameBuilder();
+            sanBuilder.AddIpAddress(IPAddress.Loopback);
+            sanBuilder.AddIpAddress(IPAddress.IPv6Loopback);
+            sanBuilder.AddDnsName("localhost");
+            var rsa = RSA.Create();
+
+            var certRequest = new CertificateRequest("CN=localhost", rsa, HashAlgorithmName.SHA512, RSASignaturePadding.Pkcs1);
+
+            certRequest.CertificateExtensions.Add(
+                new X509KeyUsageExtension(X509KeyUsageFlags.DataEncipherment | X509KeyUsageFlags.KeyEncipherment | X509KeyUsageFlags.DigitalSignature, false));
+
+            certRequest.CertificateExtensions.Add(
+                new X509EnhancedKeyUsageExtension(
+                    new OidCollection { new Oid(oid) }, false));
+
+            certRequest.CertificateExtensions.Add(sanBuilder.Build());
+
+            var certificate = certRequest.CreateSelfSigned(DateTimeOffset.Now.AddMinutes(-10), DateTimeOffset.Now.AddMinutes(10));
+            var pfxCertificate = new X509Certificate2(certificate.Export(X509ContentType.Pfx), (string)null, X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.Exportable);
+            
+            return pfxCertificate;
+        }
+
+        private async Task<IMqttClient> ConnectClientAsync(TestEnvironment testEnvironment, Func<MqttClientCertificateValidationEventArgs, bool> certValidator)
+        {
+            var clientOptionsBuilder = testEnvironment.Factory.CreateClientOptionsBuilder();
+            clientOptionsBuilder
+                .WithClientId(Guid.NewGuid().ToString())
+                .WithTcpServer("localhost", 8883)
+                .WithTls(tls =>
+                {
+                    tls.UseTls = true;
+                    tls.SslProtocol = SslProtocols.Tls12;
+                    tls.CertificateValidationHandler = certValidator;
+                });
+
+            var clientOptions = clientOptionsBuilder.Build();
+            return await testEnvironment.ConnectClient(clientOptions);
+        }
+
+        [TestMethod]
+        public async Task Tls_Swap_Test()
+        {
+            var testEnvironment = CreateTestEnvironment(MQTTnet.Formatter.MqttProtocolVersion.V500);
+            var serverOptionsBuilder = testEnvironment.Factory.CreateServerOptionsBuilder();
+
+            var firstOid = "1.3.6.1.5.5.7.3.1";
+            var secondOid = "1.3.6.1.5.5.7.3.2";
+
+            var certificateProvider = new CertificateProvider
+            {
+                CurrentCertificate = CreateCertificate(firstOid)
+            };
+
+            serverOptionsBuilder
+                .WithoutDefaultEndpoint()
+                .WithEncryptedEndpoint()
+                .WithEncryptionSslProtocol(SslProtocols.Tls12)
+                .WithEncryptionCertificate(certificateProvider);
+
+            var serverOptions = serverOptionsBuilder.Build();
+
+            var server = testEnvironment.CreateServer(serverOptions);
+
+            var publishedCount = 0;
+            server.InterceptingPublishAsync += args =>
+            {
+                Interlocked.Increment(ref publishedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await server.StartAsync();
+     
+            var firstClient = await ConnectClientAsync(testEnvironment, args =>
+            {
+                Assert.AreEqual(firstOid, ((X509Certificate2)args.Certificate).Extensions.OfType<X509EnhancedKeyUsageExtension>().First().EnhancedKeyUsages[0].Value);
+                return true;
+            });
+
+            var firstClientReceivedCount = 0;
+            firstClient.ApplicationMessageReceivedAsync += args =>
+            {
+                Interlocked.Increment(ref firstClientReceivedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await firstClient.SubscribeAsync("TestTopic1");
+
+            await firstClient.PublishAsync(new MqttApplicationMessage
+                {
+                    Topic = "TestTopic1",
+                    Payload = new byte[] { 1, 2, 3, 4}
+                });
+
+            await testEnvironment.Server.InjectApplicationMessage(new InjectedMqttApplicationMessage(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic1",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                }));
+
+            certificateProvider.CurrentCertificate = CreateCertificate(secondOid);
+
+            // Validate that the certificate was switched
+            var secondClient = await ConnectClientAsync(testEnvironment, args =>
+            {
+                Assert.AreEqual(secondOid, ((X509Certificate2)args.Certificate).Extensions.OfType<X509EnhancedKeyUsageExtension>().First().EnhancedKeyUsages[0].Value);
+                return true;
+            });
+
+            var secondClientReceivedCount = 0;
+            secondClient.ApplicationMessageReceivedAsync += args =>
+            {
+                Interlocked.Increment(ref secondClientReceivedCount);
+
+                return Task.CompletedTask;
+            };
+
+            await secondClient.SubscribeAsync("TestTopic2");
+
+            await firstClient.PublishAsync(new MqttApplicationMessage
+                {
+                    Topic = "TestTopic2",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                });
+
+            await testEnvironment.Server.InjectApplicationMessage(new InjectedMqttApplicationMessage(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic2",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                }));
+
+            // Ensure first client still works
+            await firstClient.PublishAsync(new MqttApplicationMessage
+            {
+                Topic = "TestTopic1",
+                Payload = new byte[] { 1, 2, 3, 4 }
+            });
+
+            await testEnvironment.Server.InjectApplicationMessage(new InjectedMqttApplicationMessage(
+                new MqttApplicationMessage
+                {
+                    Topic = "TestTopic1",
+                    Payload = new byte[] { 1, 2, 3, 4 }
+                }));
+
+            await Task.Delay(1000);
+
+            Assert.AreEqual(6, publishedCount);
+            Assert.AreEqual(4, firstClientReceivedCount);
+            Assert.AreEqual(2, secondClientReceivedCount);
+
+            await server.StopAsync();
+        }
+
+
+        private class CertificateProvider : ICertificateProvider
+        {
+
+            public X509Certificate2 CurrentCertificate { get; set; }
+
+            public X509Certificate2 GetCertificate()
+                => CurrentCertificate;
+
+        }
+
+    }
+}
+#endif

Source/MQTTnet/Implementations/MqttTcpServerAdapter.cs

@@ -14,6 +14,7 @@ using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Internal;
+using MQTTnet.Certificates;
 
 namespace MQTTnet.Implementations
 {
@@ -38,7 +39,7 @@ namespace MQTTnet.Implementations
 
             if (options.DefaultEndpointOptions.IsEnabled)
             {
-                RegisterListeners(options.DefaultEndpointOptions, null, logger, _cancellationTokenSource.Token);
+                RegisterListeners(options.DefaultEndpointOptions, logger, _cancellationTokenSource.Token);
             }
 
             if (options.TlsEndpointOptions?.IsEnabled == true)
@@ -48,13 +49,7 @@ namespace MQTTnet.Implementations
                     throw new ArgumentException("TLS certificate is not set.");
                 }
 
-                var tlsCertificate = options.TlsEndpointOptions.CertificateProvider.GetCertificate();
-                if (!tlsCertificate.HasPrivateKey)
-                {
-                    throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
-                }
-
-                RegisterListeners(options.TlsEndpointOptions, tlsCertificate, logger, _cancellationTokenSource.Token);
+                RegisterListeners(options.TlsEndpointOptions, logger, _cancellationTokenSource.Token);
             }
 
             return CompletedTask.Instance;
@@ -91,11 +86,12 @@ namespace MQTTnet.Implementations
             }
         }
 
-        void RegisterListeners(MqttServerTcpEndpointBaseOptions tcpEndpointOptions, X509Certificate2 tlsCertificate, IMqttNetLogger logger, CancellationToken cancellationToken)
+        void RegisterListeners(MqttServerTcpEndpointBaseOptions tcpEndpointOptions, IMqttNetLogger logger, CancellationToken cancellationToken)
         {
+
             if (!tcpEndpointOptions.BoundInterNetworkAddress.Equals(IPAddress.None))
             {
-                var listenerV4 = new MqttTcpServerListener(AddressFamily.InterNetwork, _serverOptions, tcpEndpointOptions, tlsCertificate, logger)
+                var listenerV4 = new MqttTcpServerListener(AddressFamily.InterNetwork, _serverOptions, tcpEndpointOptions, logger)
                 {
                     ClientHandler = OnClientAcceptedAsync
                 };
@@ -108,7 +104,7 @@ namespace MQTTnet.Implementations
 
             if (!tcpEndpointOptions.BoundInterNetworkV6Address.Equals(IPAddress.None))
             {
-                var listenerV6 = new MqttTcpServerListener(AddressFamily.InterNetworkV6, _serverOptions, tcpEndpointOptions, tlsCertificate, logger)
+                var listenerV6 = new MqttTcpServerListener(AddressFamily.InterNetworkV6, _serverOptions, tcpEndpointOptions, logger)
                 {
                     ClientHandler = OnClientAcceptedAsync
                 };

Source/MQTTnet/Implementations/MqttTcpServerListener.cs

@@ -4,6 +4,7 @@
 
 #if !WINDOWS_UWP
 using MQTTnet.Adapter;
+using MQTTnet.Certificates;
 using MQTTnet.Diagnostics;
 using MQTTnet.Formatter;
 using MQTTnet.Internal;
@@ -27,7 +28,7 @@ namespace MQTTnet.Implementations
         readonly MqttServerOptions _serverOptions;
         readonly MqttServerTcpEndpointBaseOptions _options;
         readonly MqttServerTlsTcpEndpointOptions _tlsOptions;
-        readonly X509Certificate2 _tlsCertificate;
+        X509Certificate2 _tlsCertificate;
 
         CrossPlatformSocket _socket;
         IPEndPoint _localEndPoint;
@@ -36,19 +37,18 @@ namespace MQTTnet.Implementations
             AddressFamily addressFamily,
             MqttServerOptions serverOptions,
             MqttServerTcpEndpointBaseOptions tcpEndpointOptions,
-            X509Certificate2 tlsCertificate,
             IMqttNetLogger logger)
         {
             _addressFamily = addressFamily;
             _serverOptions = serverOptions ?? throw new ArgumentNullException(nameof(serverOptions));
             _options = tcpEndpointOptions ?? throw new ArgumentNullException(nameof(tcpEndpointOptions));
-            _tlsCertificate = tlsCertificate;
             _rootLogger = logger;
             _logger = logger.WithSource(nameof(MqttTcpServerListener));
 
             if (_options is MqttServerTlsTcpEndpointOptions tlsOptions)
             {
                 _tlsOptions = tlsOptions;
+                _tlsCertificate = _tlsOptions.CertificateProvider.GetCertificate();
             }
         }
 
@@ -194,8 +194,26 @@ namespace MQTTnet.Implementations
                 stream = clientSocket.GetStream();
                 X509Certificate2 clientCertificate = null;
 
+                if (_tlsOptions.CertificateProvider != null)
+                {
+                    var tlsCertificate = _tlsOptions.CertificateProvider.GetCertificate();
+                    if (tlsCertificate != _tlsCertificate)
+                    {
+                        var oldTlsCertificate = _tlsCertificate;
+                        _tlsCertificate = tlsCertificate;
+#if !NET452
+                        oldTlsCertificate.Dispose();
+#endif
+                    }
+                }
+
                 if (_tlsCertificate != null)
                 {
+                    if (!_tlsCertificate.HasPrivateKey)
+                    {
+                        throw new InvalidOperationException("The certificate for TLS encryption must contain the private key.");
+                    }
+
                     var sslStream = new SslStream(stream, false, _tlsOptions.RemoteCertificateValidationCallback);
 
                     #if NETCOREAPP3_1_OR_GREATER

Source/MQTTnet/Server/Options/MqttServerOptionsBuilder.cs

@@ -198,6 +198,18 @@ namespace MQTTnet.Server
             _options.TlsEndpointOptions.CertificateProvider = new X509CertificateProvider(certificate);
             return this;
         }
+
+        public MqttServerOptionsBuilder WithEncryptionCertificate(ICertificateProvider certificateProvider)
+        {
+            if (certificateProvider == null)
+            {
+                throw new ArgumentNullException(nameof(certificateProvider));
+            }
+
+            _options.TlsEndpointOptions.CertificateProvider = certificateProvider;
+
+            return this;
+        }
 #endif
     }
 }