Task<T>.WithCancellationToken extension for async methods that do not accept a CancellationToken parameter

gistfile1.txt

public static class TaskExtensions
{
	public static async Task<T?> WithCancellationToken<T>(this Task<T> source, CancellationToken cancellationToken)
	{
		var cancellationTask = new TaskCompletionSource<bool>();
		cancellationToken.Register(() => cancellationTask.SetCanceled());

		_ = await Task.WhenAny(source, cancellationTask.Task);

		if (cancellationToken.IsCancellationRequested)
			return default;
		return source.Result;
	}
}