cancel_05.cs

public async Task SendAsync(CancellationToken cancellationToken = default)
{
    using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
    cts.CancelAfter(Timeout);

    try
    {
        await SendCoreAsync(cts.Token);
    }
    catch (OperationCanceledException ex) when (ex.CancellationToken == cts.Token)
    {
        if (cancellationToken.IsCancellationRequested)
        {
            // Error reason is argument CancellationToken, hold token in new OperationCanceledException
            throw new OperationCanceledException(ex.Message, ex, cancellationToken);
        }
        else
        {
            // Error reason is timeout, throw TimeoutException(or any custom exception)
            throw new TimeoutException($"The request was canceled due to the configured Timeout of {Timeout.TotalSeconds} seconds elapsing.", ex);
        }
    }
}