Added TLS1.2 support to client and server.

Added MqttClientSslChannel and MqttServerSslChannel which both utilize
an SSL stream.  Added options to both MqttCLientOptions and
MqttServerOptions.  I was unable to update the code in
MQTTnet.UniversalWindows due to my lack of Windows 10.

Frameworks/MQTTnet.NetCoreApp/MqttClientFactory.cs

@@ -1,5 +1,6 @@
 using System;
 using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Channel;
 using MQTTnet.Core.Client;
 using MQTTnet.Core.Serializer;
 
@@ -11,7 +12,11 @@ namespace MQTTnet
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+            return new MqttClient(options,
+                // The cast to IMqttCommunicationChannel is required... Roslyn is too stupid to
+                // figure out how to cast back to the base type
+                new MqttChannelCommunicationAdapter(options.UseSSL ? new MqttClientSslChannel() : (IMqttCommunicationChannel) new MqttTcpChannel(),
+                    new DefaultMqttV311PacketSerializer()));
         }
     }
 }

Frameworks/MQTTnet.NetCoreApp/MqttClientSslChannel.cs

@@ -0,0 +1,122 @@
+using System;
+using System.IO;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Security.Authentication;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Exceptions;
+
+namespace MQTTnet
+{
+    /// <summary>
+    /// Describes an SSL channel to an MQTT server.
+    /// </summary>
+    public class MqttClientSslChannel : IMqttCommunicationChannel, IDisposable
+    {
+        private readonly Socket _socket;
+        private SslStream _sslStream;
+
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public MqttClientSslChannel()
+        {
+            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/> with a predefined <paramref name="socket"/>.
+        /// </summary>
+        /// <param name="socket"></param>
+        public MqttClientSslChannel(Socket socket)
+        {
+            _socket = socket ?? throw new ArgumentNullException(nameof(socket));
+        }
+
+        /// <summary>
+        /// Asynchronously connects to the host described in the <see cref="MqttClientOptions"/>.
+        /// </summary>
+        /// <param name="options">The <see cref="MqttClientOptions"/> describing the connection.</param>
+        public async Task ConnectAsync(MqttClientOptions options)
+        {
+            try
+            {
+                await _socket.ConnectAsync(options.Server, options.Port);
+
+                NetworkStream ns = new NetworkStream(_socket, true);
+                _sslStream = new SslStream(ns);
+
+                await _sslStream.AuthenticateAsClientAsync(options.Server, null, SslProtocols.Tls12, false);
+
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously disconnects the client from the server.
+        /// </summary>
+        public Task DisconnectAsync()
+        {
+            try
+            {
+                _socket.Dispose();
+                return Task.FromResult(0);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously writes a sequence of bytes to the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write data from.</param>
+        public async Task WriteAsync(byte[] buffer)
+        {
+            if (buffer == null)
+                throw new ArgumentNullException(nameof(buffer));
+
+            try
+            {
+                await _sslStream.WriteAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously reads a sequence of bytes from the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write the data into.</param>
+        public async Task ReadAsync(byte[] buffer)
+        {
+            try
+            {
+                await _sslStream.ReadAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Releases all resources used by the <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public void Dispose()
+        {
+            _sslStream?.Dispose();
+            _socket?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetCoreApp/MqttServerFactory.cs

@@ -1,4 +1,5 @@
 using System;
+using MQTTnet.Core.Adapter;
 using MQTTnet.Core.Server;
 
 namespace MQTTnet
@@ -9,7 +10,8 @@ namespace MQTTnet
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            return new MqttServer(options, new MqttServerAdapter());
+            // The cast to IMqttServerAdapter is required... stupidly...
+            return new MqttServer(options, options.UseSSL ? (IMqttServerAdapter)new MqttSslServerAdapter() : new MqttServerAdapter());
         }
     }
 }

Frameworks/MQTTnet.NetCoreApp/MqttServerSslChannel.cs

@@ -0,0 +1,123 @@
+using System;
+using System.IO;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Exceptions;
+
+namespace MQTTnet
+{
+    /// <summary>
+    /// Describes an SSL channel to a client.
+    /// </summary>
+    public class MqttServerSslChannel : IMqttCommunicationChannel, IDisposable
+    {
+        private readonly Socket _socket;
+        private readonly SslStream _sslStream;
+        private readonly X509Certificate2 _cert;
+        
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/> with a predefined <paramref name="socket"/>.
+        /// </summary>
+        /// <param name="socket">The client socket.</param>
+        /// <param name="cert">The X509 certificate used to authenticate as a server.</param>
+        public MqttServerSslChannel(Socket socket, X509Certificate2 cert)
+        {
+            _socket = socket ?? throw new ArgumentNullException(nameof(socket));
+            _cert = cert ?? throw new ArgumentNullException(nameof(cert));
+
+            if (_socket.Connected)
+            {
+                NetworkStream ns = new NetworkStream(_socket, true);
+                _sslStream = new SslStream(ns);
+            }
+        }
+
+        public async Task Authenticate()
+        {
+            await _sslStream.AuthenticateAsServerAsync(_cert, false, SslProtocols.Tls12, false);
+        }
+
+        /// <summary>
+        /// Asynchronously connects to the client described in the <see cref="MqttClientOptions"/>.
+        /// </summary>
+        /// <param name="options">The <see cref="MqttClientOptions"/> describing the connection.</param>
+        public async Task ConnectAsync(MqttClientOptions options)
+        {
+            try
+            {
+                await _socket.ConnectAsync(options.Server, options.Port);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously disconnects the client from the server.
+        /// </summary>
+        public Task DisconnectAsync()
+        {
+            try
+            {
+                _socket.Dispose();
+                return Task.FromResult(0);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously writes a sequence of bytes to the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write data from.</param>
+        public async Task WriteAsync(byte[] buffer)
+        {
+            if (buffer == null)
+                throw new ArgumentNullException(nameof(buffer));
+
+            try
+            {
+                await _sslStream.WriteAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously reads a sequence of bytes from the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write the data into.</param>
+        public async Task ReadAsync(byte[] buffer)
+        {
+            try
+            {
+                await _sslStream.ReadAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Releases all resources used by the <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public void Dispose()
+        {
+            _sslStream?.Dispose();
+            _socket?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetCoreApp/MqttSslServerAdapter.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Net;
+using System.Net.Sockets;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Serializer;
+using MQTTnet.Core.Server;
+
+namespace MQTTnet
+{
+    public class MqttSslServerAdapter : IMqttServerAdapter, IDisposable
+    {
+        private CancellationTokenSource _cancellationTokenSource;
+        private Socket _socket;
+        private X509Certificate2 _x590Certificate2;
+
+        public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
+
+        public void Start(MqttServerOptions options)
+        {
+            if (_socket != null) throw new InvalidOperationException("Server is already started.");
+
+            _cancellationTokenSource = new CancellationTokenSource();
+
+            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+            _socket.Bind(new IPEndPoint(IPAddress.Any, options.Port));
+            _socket.Listen(options.ConnectionBacklog);
+
+            Task.Run(async () => await AcceptConnectionsAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
+
+            _x590Certificate2 = new X509Certificate2(options.CertificatePath);
+        }
+
+        public void Stop()
+        {
+            _cancellationTokenSource?.Dispose();
+            _cancellationTokenSource = null;
+
+            _socket?.Dispose();
+            _socket = null;
+        }
+
+        public void Dispose()
+        {
+            Stop();
+        }
+
+        private async Task AcceptConnectionsAsync(CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                var clientSocket = await _socket.AcceptAsync();
+
+                MqttServerSslChannel mssc = new MqttServerSslChannel(clientSocket, _x590Certificate2);
+                await mssc.Authenticate();
+
+                var clientAdapter = new MqttChannelCommunicationAdapter(mssc, new DefaultMqttV311PacketSerializer());
+                ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
+            }
+        }
+    }
+}

Frameworks/MQTTnet.NetFramework/MQTTnet.NetFramework.csproj

@@ -103,6 +103,9 @@
     <Compile Include="MqttClientFactory.cs" />
     <Compile Include="MqttServerAdapter.cs" />
     <Compile Include="MqttServerFactory.cs" />
+    <Compile Include="MqttClientSslChannel.cs" />
+    <Compile Include="MqttServerSslChannel.cs" />
+    <Compile Include="MqttSslServerAdapter.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="MqttTcpChannel.cs" />
   </ItemGroup>

Frameworks/MQTTnet.NetFramework/MqttClientFactory.cs

@@ -1,5 +1,6 @@
 using System;
 using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Channel;
 using MQTTnet.Core.Client;
 using MQTTnet.Core.Serializer;
 
@@ -10,8 +11,12 @@ namespace MQTTnet
         public MqttClient CreateMqttClient(MqttClientOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
-
-            return new MqttClient(options, new MqttChannelCommunicationAdapter(new MqttTcpChannel(), new DefaultMqttV311PacketSerializer()));
+            
+            return new MqttClient(options,
+                // The cast to IMqttCommunicationChannel is required... Roslyn is too stupid to
+                // figure out how to cast back to the base type
+                new MqttChannelCommunicationAdapter(options.UseSSL ? new MqttClientSslChannel() : (IMqttCommunicationChannel)new MqttTcpChannel(),
+                    new DefaultMqttV311PacketSerializer()));
         }
     }
 }

Frameworks/MQTTnet.NetFramework/MqttClientSslChannel.cs

@@ -0,0 +1,122 @@
+using System;
+using System.IO;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Security.Authentication;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Exceptions;
+
+namespace MQTTnet
+{
+    /// <summary>
+    /// Describes an SSL channel to an MQTT server.
+    /// </summary>
+    public class MqttClientSslChannel : IMqttCommunicationChannel, IDisposable
+    {
+        private readonly Socket _socket;
+        private SslStream _sslStream;
+
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public MqttClientSslChannel()
+        {
+            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/> with a predefined <paramref name="socket"/>.
+        /// </summary>
+        /// <param name="socket"></param>
+        public MqttClientSslChannel(Socket socket)
+        {
+            _socket = socket ?? throw new ArgumentNullException(nameof(socket));
+        }
+
+        /// <summary>
+        /// Asynchronously connects to the host described in the <see cref="MqttClientOptions"/>.
+        /// </summary>
+        /// <param name="options">The <see cref="MqttClientOptions"/> describing the connection.</param>
+        public async Task ConnectAsync(MqttClientOptions options)
+        {
+            try
+            {
+                await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, options.Server, options.Port,
+                    null);
+
+                NetworkStream ns = new NetworkStream(_socket, true);
+                _sslStream = new SslStream(ns);
+
+                await _sslStream.AuthenticateAsClientAsync(options.Server, null, SslProtocols.Tls12, false);
+
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously disconnects the client from the server.
+        /// </summary>
+        public async Task DisconnectAsync()
+        {
+            try
+            {
+                await Task.Factory.FromAsync(_socket.BeginDisconnect, _socket.EndDisconnect, true, null);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously writes a sequence of bytes to the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write data from.</param>
+        public async Task WriteAsync(byte[] buffer)
+        {
+            if (buffer == null)
+                throw new ArgumentNullException(nameof(buffer));
+
+            try
+            {
+                await _sslStream.WriteAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously reads a sequence of bytes from the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write the data into.</param>
+        public async Task ReadAsync(byte[] buffer)
+        {
+            try
+            {
+                await _sslStream.ReadAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Releases all resources used by the <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public void Dispose()
+        {
+            _sslStream?.Dispose();
+            _socket?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetFramework/MqttServerFactory.cs

@@ -1,4 +1,5 @@
 using System;
+using MQTTnet.Core.Adapter;
 using MQTTnet.Core.Server;
 
 namespace MQTTnet
@@ -8,8 +9,9 @@ namespace MQTTnet
         public MqttServer CreateMqttServer(MqttServerOptions options)
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
-
-            return new MqttServer(options, new MqttServerAdapter());
+            
+            // The cast to IMqttServerAdapter is required... stupidly...
+            return new MqttServer(options, options.UseSSL ? (IMqttServerAdapter) new MqttSslServerAdapter() : new MqttServerAdapter());
         }
     }
 }

Frameworks/MQTTnet.NetFramework/MqttServerSslChannel.cs

@@ -0,0 +1,123 @@
+using System;
+using System.IO;
+using System.Net.Security;
+using System.Net.Sockets;
+using System.Security.Authentication;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading.Tasks;
+using MQTTnet.Core.Channel;
+using MQTTnet.Core.Client;
+using MQTTnet.Core.Exceptions;
+
+namespace MQTTnet
+{
+    /// <summary>
+    /// Describes an SSL channel to a client.
+    /// </summary>
+    public class MqttServerSslChannel : IMqttCommunicationChannel, IDisposable
+    {
+        private readonly Socket _socket;
+        private SslStream _sslStream;
+        private X509Certificate2 _cert;
+        
+        /// <summary>
+        /// Creates a new <see cref="MqttClientSslChannel"/> with a predefined <paramref name="socket"/>.
+        /// </summary>
+        /// <param name="socket">The client socket.</param>
+        /// <param name="cert">The X509 certificate used to authenticate as a server.</param>
+        public MqttServerSslChannel(Socket socket, X509Certificate2 cert)
+        {
+            _socket = socket ?? throw new ArgumentNullException(nameof(socket));
+            _cert = cert ?? throw new ArgumentNullException(nameof(cert));
+
+            if (_socket.Connected)
+            {
+                NetworkStream ns = new NetworkStream(_socket, true);
+                _sslStream = new SslStream(ns);
+            }
+        }
+
+        public async Task Authenticate()
+        {
+            await _sslStream.AuthenticateAsServerAsync(_cert, false, SslProtocols.Tls12, false);
+        }
+
+        /// <summary>
+        /// Asynchronously connects to the client described in the <see cref="MqttClientOptions"/>.
+        /// </summary>
+        /// <param name="options">The <see cref="MqttClientOptions"/> describing the connection.</param>
+        public async Task ConnectAsync(MqttClientOptions options)
+        {
+            try
+            {
+                await Task.Factory.FromAsync(_socket.BeginConnect, _socket.EndConnect, options.Server, options.Port,
+                    null);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously disconnects the client from the server.
+        /// </summary>
+        public async Task DisconnectAsync()
+        {
+            try
+            {
+                await Task.Factory.FromAsync(_socket.BeginDisconnect, _socket.EndDisconnect, true, null);
+            }
+            catch (SocketException exception)
+            {
+                throw new MqttCommunicationException(exception);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously writes a sequence of bytes to the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write data from.</param>
+        public async Task WriteAsync(byte[] buffer)
+        {
+            if (buffer == null)
+                throw new ArgumentNullException(nameof(buffer));
+
+            try
+            {
+                await _sslStream.WriteAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Asynchronously reads a sequence of bytes from the socket.
+        /// </summary>
+        /// <param name="buffer">The buffer to write the data into.</param>
+        public async Task ReadAsync(byte[] buffer)
+        {
+            try
+            {
+                await _sslStream.ReadAsync(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex)
+                when (ex is SocketException || ex is IOException)
+            {
+                throw new MqttCommunicationException(ex);
+            }
+        }
+
+        /// <summary>
+        /// Releases all resources used by the <see cref="MqttClientSslChannel"/>.
+        /// </summary>
+        public void Dispose()
+        {
+            _sslStream?.Dispose();
+            _socket?.Dispose();
+        }
+    }
+}

Frameworks/MQTTnet.NetFramework/MqttSslServerAdapter.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Net;
+using System.Net.Sockets;
+using System.Security.Cryptography.X509Certificates;
+using System.Threading;
+using System.Threading.Tasks;
+using MQTTnet.Core.Adapter;
+using MQTTnet.Core.Serializer;
+using MQTTnet.Core.Server;
+
+namespace MQTTnet
+{
+    public class MqttSslServerAdapter : IMqttServerAdapter, IDisposable
+    {
+        private CancellationTokenSource _cancellationTokenSource;
+        private Socket _socket;
+        private X509Certificate2 _x590Certificate2;
+
+        public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;
+
+        public void Start(MqttServerOptions options)
+        {
+            if (_socket != null) throw new InvalidOperationException("Server is already started.");
+
+            _cancellationTokenSource = new CancellationTokenSource();
+
+            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
+            _socket.Bind(new IPEndPoint(IPAddress.Any, options.Port));
+            _socket.Listen(options.ConnectionBacklog);
+
+            Task.Run(async () => await AcceptConnectionsAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
+
+            _x590Certificate2 = new X509Certificate2(options.CertificatePath);
+        }
+
+        public void Stop()
+        {
+            _cancellationTokenSource?.Dispose();
+            _cancellationTokenSource = null;
+
+            _socket?.Dispose();
+            _socket = null;
+        }
+
+        public void Dispose()
+        {
+            Stop();
+        }
+
+        private async Task AcceptConnectionsAsync(CancellationToken cancellationToken)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                var clientSocket = await Task.Factory.FromAsync(_socket.BeginAccept, _socket.EndAccept, null);
+
+                MqttServerSslChannel mssc = new MqttServerSslChannel(clientSocket, _x590Certificate2);
+                await mssc.Authenticate();
+
+                var clientAdapter = new MqttChannelCommunicationAdapter(mssc, new DefaultMqttV311PacketSerializer());
+                ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
+            }
+        }
+    }
+}

MQTTnet.Core/Client/MqttClientOptions.cs

@@ -19,5 +19,24 @@ namespace MQTTnet.Core.Client
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(5);
 
         public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
+
+        /// <summary>
+        /// Use SSL to communicate with the MQTT server.
+        /// </summary>
+        /// <remarks>Setting this value to <c>true</c> will also set <see cref="Port"/> to <c>8883</c> if its value was <c>1883</c> (not set).</remarks>
+        public bool UseSSL
+        {
+            get => _useSSL;
+            set
+            {
+                // Automatically set the port to the MQTT SSL port (8883) if it wasn't set already
+                if (value && Port == 1883)
+                    Port = 8883;
+
+                _useSSL = value;
+            }
+        }
+
+        private bool _useSSL;
     }
 }

MQTTnet.Core/Server/MqttServerOptions.cs

@@ -13,5 +13,12 @@ namespace MQTTnet.Core.Server
         public TimeSpan DefaultCommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
 
         public Func<MqttConnectPacket, MqttConnectReturnCode> ConnectionValidator { get; set; }
+
+        public bool UseSSL = false;
+
+        /// <summary>
+        /// The path to the X509 SSL certificate.
+        /// </summary>
+        public string CertificatePath = string.Empty;
     }
 }