Initial commit.

Shared/SignalR/ClientTracker.cs

@@ -0,0 +1,18 @@
+using System.Collections.Concurrent;
+
+namespace ClientApiPoC.Shared.SignalR {
+    public class ClientTracker {
+        private ConcurrentDictionary<string, string> _knownClientIds = new();
+
+        public ICollection<string> CurrentClientIds => _knownClientIds.Values;
+
+        public bool TryAddClientId(string clientId) {
+            if (string.IsNullOrWhiteSpace(clientId)) throw new ArgumentNullException(nameof(clientId));
+            return _knownClientIds.TryAdd(clientId, clientId);
+        }
+
+        public bool TryRemoveClientId(string clientId) {
+            return _knownClientIds.TryRemove(clientId, out _);
+        }
+    }
+}