TaskExtensions.cs

static class TaskExtensions
{
    public static Task AsTask(this CancellationToken cancellationToken, bool useContext = false)
    {
        var tcs = new TaskCompletionSource<object>();
        cancellationToken.Register(() => tcs.TrySetCanceled(), useSynchronizationContext: useContext);
        return tcs.Task;
    }
}