Fix support for enhanced authentication (#2132)

* Implement enhanced authentication for client and server.

* Update samples

* Add abstraction layer

* Merge master

* Use dedicated class for public API.

* Update release notes

* Rename methods to fit naming scheme

* Fix unit tests and samples

Source/MQTTnet.Server/EnhancedAuthentication/ExchangeEnhancedAuthenticationResultFactory.cs

@@ -0,0 +1,34 @@
+using MQTTnet.Packets;
+
+namespace MQTTnet.Server.EnhancedAuthentication;
+
+public static class ExchangeEnhancedAuthenticationResultFactory
+{
+    public static ExchangeEnhancedAuthenticationResult Create(MqttAuthPacket authPacket)
+    {
+        ArgumentNullException.ThrowIfNull(authPacket);
+
+        return new ExchangeEnhancedAuthenticationResult
+        {
+            AuthenticationData = authPacket.AuthenticationData,
+
+            ReasonString = authPacket.ReasonString,
+            UserProperties = authPacket.UserProperties
+        };
+    }
+
+    public static ExchangeEnhancedAuthenticationResult Create(MqttDisconnectPacket disconnectPacket)
+    {
+        ArgumentNullException.ThrowIfNull(disconnectPacket);
+
+        return new ExchangeEnhancedAuthenticationResult
+        {
+            AuthenticationData = null,
+            ReasonString = disconnectPacket.ReasonString,
+            UserProperties = disconnectPacket.UserProperties
+
+            // SessionExpiryInterval makes no sense because the connection is not yet made!
+            // ServerReferences makes no sense when the client initiated a DISCONNECT!
+        };
+    }
+}