Async WCF Operation Cancellation Pattern

Service.cs

[ServiceContract]
public interface IMyService
{
  [OperationContract]
  Task DoExpensiveOperation(Guid requestId);
  
  [OperationContract(IsOneWay=true)]
  void CancelExpensiveOperation(Guid requestId);
}

public class MyService : IMyService
{
  private readonly ConcurrentDictionary<Guid, CancellationTokenSource> _requests = new ConcurrentDictionary<Guid, CancellationTokenSource>();
  
  public Task DoExpensiveOperation(Guid requestId)
  {
    var cancellationTokenSource = _requests.AddOrUpdate(requestId, u => new CancellationTokenSource(), (u, source) => source);
    try
    {
    	// TODO: await call to async method sending over the cancellationTokenSource.Token
    }
    finally
    {
      _requests.TryRemove(requestId, out _);
    }
  }
  
  public void CancelExpensiveOperation(Guid requestId)
  {
    if (_requests.TryRemove(requestId, out var cancellationTokenSource))
    {
      cancellationTokenSource.Cancel();
    }
  }
}

public class MyServiceClientProxy
{
  private readonly MyServiceClient _myServiceClient;
  
  public MyServiceClientProxy(MyServiceClient myServiceClient)
  {
    _myServiceClient = myServiceClient;
  }
  
  public Task DoExpensiveOperation(CancellationToken cancellationToken)
  {
    var requestId = Guid.New();
    cancellationToken.Register(() => _myServiceClient.CancelExpensiveOperation(requestId));
    return _myServiceClient.DoExpensiveOperation(requestId);
  }
  
}