UniTaskWrapper.cs

public void Foo(Action<int> callback)
{

}

#region UniTask wrapper
private CancellationTokenSource _source;

public async void FooAsync()
{
    using(_source = new CancellationTokenSource())
    {
        try
        {
            var source = new UniTaskCompletionSource<int>();
            using (_source.Token.Register(() => source.TrySetCanceled()))
            {
                Foo(x => source.TrySetResult(x));
                var result = await source.Task;
                Debug.Log(result);
            }
        }
        catch (OperationCanceledException e)
        {
            Debug.LogException(e);
        }
    }
}

public void Cancel()
{
    _source.Cancel();
}
#endregion