title: make files uploaded with carrierwave accessible only to activeadmin users
body: <p>I am uploading some files with carrierwave</p>
  <pre><code>class Document &lt; ApplicationRecord
    mount_uploader :pdf_file, MyPdfUploader
  
  class MyPdfUploader &lt; CarrierWave::Uploader::Base
    storage :file
  
  def store_dir
    &quot;uploads/#{model.class.to_s.underscore}/#{model.id}&quot;
  end
  </code></pre>
  <p>I now want to have access to this file only for activeadmin authenticated users.
  What is the proper way to achieve this?</p>