Squashed commit of the following:

commit 469caf656e
Author: Christian <6939810+chkr1011@users.noreply.github.com>
Date:   Sun Jul 31 10:55:40 2022 +0200

    Fix build errors.

commit 42402fba04
Author: Christian <6939810+chkr1011@users.noreply.github.com>
Date:   Sun Jul 31 10:22:23 2022 +0200

    Allow interception of injected application messages.

commit a0dc8ab0d7
Author: William Lee <31092948+william19821101@users.noreply.github.com>
Date:   Sun Jul 31 15:50:14 2022 +0800

    Update Server_Simple_Samples.cs (#1474)

    Change e.UserName to e.Username

.github/workflows/ReleaseNotes.md

@@ -1,4 +1,5 @@
-* [Client] Added support for passing the local endpoint which should be used (network card).
+* [Client] Added support for passing the local endpoint (network card) which should be used (#1311).
 * [Client] Exposed _PackageIdentifier_ in _MqttApplicationMessageReceivedEventArgs_ (thanks to @koepalex, #1466).
 * [Server] Added a new event (_ClientAcknowledgedPublishPacketAsync_) which is fired whenever a client acknowledges a PUBLISH packet (QoS 1 and 2, #487).
 * [Server] Exposed channel adapter (HTTP context etc.) in connection validation (#1125).
+* [Server] The event _InterceptingPublishAsync_ is now also called for injected application messages (#Jeanot-Zubler).

Samples/Server/Server_Simple_Samples.cs

@@ -138,7 +138,7 @@ public static class Server_Simple_Samples
                     e.ReasonCode = MqttConnectReasonCode.ClientIdentifierNotValid;
                 }
 
-                if (e.UserName != "ValidUser")
+                if (e.Username != "ValidUser")
                 {
                     e.ReasonCode = MqttConnectReasonCode.BadUserNameOrPassword;
                 }
@@ -216,4 +216,4 @@ public static class Server_Simple_Samples
             }
         }
     }
-}
+}

Source/MQTTnet/Server/Internal/MqttServerEventContainer.cs

@@ -26,6 +26,7 @@ namespace MQTTnet.Server
         public AsyncEvent<InterceptingPacketEventArgs> InterceptingOutboundPacketEvent { get; } = new AsyncEvent<InterceptingPacketEventArgs>();
 
         public AsyncEvent<InterceptingPublishEventArgs> InterceptingPublishEvent { get; } = new AsyncEvent<InterceptingPublishEventArgs>();
+        
         public AsyncEvent<InterceptingSubscriptionEventArgs> InterceptingSubscriptionEvent { get; } = new AsyncEvent<InterceptingSubscriptionEventArgs>();
 
         public AsyncEvent<InterceptingUnsubscriptionEventArgs> InterceptingUnsubscriptionEvent { get; } = new AsyncEvent<InterceptingUnsubscriptionEventArgs>();

Source/MQTTnet/Server/MqttServer.cs

@@ -3,6 +3,8 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -19,7 +21,8 @@ namespace MQTTnet.Server
     public class MqttServer : Disposable
     {
         readonly MqttServerEventContainer _eventContainer = new MqttServerEventContainer();
-        
+
+        readonly IDictionary _sessionItems = new ConcurrentDictionary<object, object>();
         readonly ICollection<IMqttServerAdapter> _adapters;
         readonly MqttNetSourceLogger _logger;
         readonly MqttServerOptions _options;
@@ -205,7 +208,7 @@ namespace MQTTnet.Server
             return _clientSessionsManager.GetSessionStatusAsync();
         }
 
-        public Task InjectApplicationMessage(InjectedMqttApplicationMessage injectedApplicationMessage)
+        public async Task InjectApplicationMessage(InjectedMqttApplicationMessage injectedApplicationMessage)
         {
             if (injectedApplicationMessage == null)
             {
@@ -221,7 +224,36 @@ namespace MQTTnet.Server
 
             ThrowIfNotStarted();
 
-            return _clientSessionsManager.DispatchApplicationMessage(injectedApplicationMessage.SenderClientId, injectedApplicationMessage.ApplicationMessage);
+            var processPublish = true;
+            var applicationMessage = injectedApplicationMessage.ApplicationMessage;
+            
+            if (_eventContainer.InterceptingPublishEvent.HasHandlers)
+            {
+                var interceptingPublishEventArgs = new InterceptingPublishEventArgs
+                {
+                    ApplicationMessage = applicationMessage,
+                    CancellationToken = _cancellationTokenSource.Token,
+                    ClientId = injectedApplicationMessage.SenderClientId,
+                    SessionItems = _sessionItems
+                };
+                    
+                await _eventContainer.InterceptingPublishEvent.InvokeAsync(interceptingPublishEventArgs).ConfigureAwait(false);
+
+                applicationMessage = interceptingPublishEventArgs.ApplicationMessage;
+                processPublish = interceptingPublishEventArgs.ProcessPublish;
+            }
+
+            if (!processPublish)
+            {
+                return;
+            }
+            
+            if (string.IsNullOrEmpty(applicationMessage.Topic))
+            {
+                throw new NotSupportedException("Injected application messages must contain a topic. Topic alias is not supported.");
+            }
+            
+            await _clientSessionsManager.DispatchApplicationMessage(injectedApplicationMessage.SenderClientId, applicationMessage).ConfigureAwait(false);
         }
 
         public async Task StartAsync()