ClientApiPoC/Shared/SignalR/TunnelHub.cs

using Microsoft.AspNetCore.SignalR;

namespace ClientApiPoC.Shared.SignalR {
    public sealed class TunnelHub : Hub {
        private ClientTracker _clientTracker;

        public TunnelHub(ClientTracker clientTracker) : base() {
            if (clientTracker == null) throw new ArgumentNullException(nameof(clientTracker));
            _clientTracker = clientTracker;
        }

        public override sealed async Task OnConnectedAsync() {
            _ = _clientTracker.TryAddClientId(this.Context.ConnectionId);
        }

        public override sealed async Task OnDisconnectedAsync(Exception exception) {
            _ = _clientTracker.TryRemoveClientId(this.Context.ConnectionId);
        }
    }
}