Switch to ManagedIdentityId for token credential authentication and cleanup unnecessary properties

Author: danielmarbach

src/ServiceControl.Transports.ASBS/ConnectionStringParser.cs

@@ -2,6 +2,7 @@
 {
     using System;
     using System.Data.Common;
+    using Azure.Identity;
     using Azure.Messaging.ServiceBus;
 
     public static class ConnectionStringParser

src/ServiceControl.Transports.ASBS/TokenCredentialAuthentication.cs

@@ -1,4 +1,5 @@
-namespace ServiceControl.Transports.ASBS
+#nullable enable
+namespace ServiceControl.Transports.ASBS
 {
     using Azure.Core;
     using Azure.Identity;
@@ -13,21 +14,17 @@ public TokenCredentialAuthentication(string fullyQualifiedNamespace)
             Credential = new DefaultAzureCredential();
         }
 
-        public TokenCredentialAuthentication(string fullyQualifiedNamespace, string clientId)
+        public TokenCredentialAuthentication(string fullyQualifiedNamespace, string? clientId)
         {
             FullyQualifiedNamespace = fullyQualifiedNamespace;
-            ClientId = clientId;
-            Credential = new ManagedIdentityCredential(clientId);
+            Credential = new ManagedIdentityCredential(clientId is not null ? ManagedIdentityId.FromUserAssignedClientId(clientId) : ManagedIdentityId.SystemAssigned);
         }
 
-        public string FullyQualifiedNamespace { get; }
+        string FullyQualifiedNamespace { get; }
 
         public TokenCredential Credential { get; }
 
-        public string ClientId { get; }
-
-        public override ServiceBusAdministrationClient BuildManagementClient()
-            => new ServiceBusAdministrationClient(FullyQualifiedNamespace, Credential);
+        public override ServiceBusAdministrationClient BuildManagementClient() => new(FullyQualifiedNamespace, Credential);
 
         public override AzureServiceBusTransport CreateTransportDefinition(ConnectionSettings connectionSettings, TopicTopology topology)
         {