The :file type is primarily meant for accepting files over interfaces. You’d add a file as an argument, and then use a change on the action to take that file and do something with it. Like you can move it from the temporary directory it is uploaded to by default when it’s a plug.upload, etc.

Really need to write a more comprehensive guide on dealing with file uploads: AshJsonApi.Plug.Parser — ash_json_api v1.7.0

Correct on the admin question, but not yet, but we would like to implement that

You can potentially use Waffle, although not something like WaffleEcto

create :create_user do
  argument :profile_photo, :file
  change fn changeset, _ ->
    Ash.Changeset.before_transaction(changeset, fn changeset, _ ->
      if upload = changeset.arguments[:file] do
         url = <upload to s3>
         Ash.Changeset.force_change_attribute(changeset, :profile_photo_url, url)
      else
         changeset
      end
    end
  end
end

It would be a welcome addition I suspect that it will be surprisingly complex but I could be wrong. Ultimately the pattern would be to fork ash_admin and then submit a PR. Everything would be done in the form component when rendering attribute inputs.