Validating file uploads when using Form Request

How do I validate file uploads in Laravel 5, when using form requests? The input fields are in the files array instead of the requests array, and it seems that the validation rules cannot access the files array.

I have tried this

 $rules = [
      'files.upload' => 'required'
    ]

However, the validator still can't detect the file field in the request.

via Chebli Mohamed