Add overload to allow passing custom request headers and cookies when connecting with WS

Source/MQTTnet/Client/MqttClientOptionsBuilder.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
+using System.Net;
 using MQTTnet.Serializer;
 
 namespace MQTTnet.Client
@@ -102,6 +104,23 @@ namespace MQTTnet.Client
             return this;
         }
 
+        public MqttClientOptionsBuilder WithWebSocketServer(string uri, MqttClientOptionsBuilderWebSocketParameters parameters)
+        {
+            if(parameters == null)
+            {
+                throw new ArgumentNullException(nameof(parameters));
+            }
+
+            _webSocketOptions = new MqttClientWebSocketOptions
+            {
+                Uri = uri,
+                RequestHeaders = parameters.RequestHeaders,
+                CookieContainer = parameters.CookierContainer
+            };
+
+            return this;
+        }
+
         public MqttClientOptionsBuilder WithTls(MqttClientOptionsBuilderTlsParameters parameters)
         {
             _tlsParameters = parameters ?? throw new ArgumentNullException(nameof(parameters));

Source/MQTTnet/Client/MqttClientOptionsBuilderWebSocketParameters.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Text;
+
+namespace MQTTnet.Client
+{
+    public class MqttClientOptionsBuilderWebSocketParameters
+    {
+        public IDictionary<string, string> RequestHeaders { get; set; }
+
+        public CookieContainer CookierContainer { get; set; }
+    }
+}