Private files result in access denied for non admin users.

Problem/Motivation

Not sure if this is by design or I'm missing something but I get an access denied message when trying to download a private file that I uploaded as part of the form submission.

Steps to reproduce

Set up a form that contains a private upload field
Login as an authorised user (non administrator)
Submit the form
View the form submission that contains the link to the private file
Click on the link and get access denied.
I can only get it to work if I give the role permission to administrate the webform and submissions which I don't want.

Proposed resolution

Allow authorised users who complete a form to download the private file in the webform submission

Remaining tasks

User interface changes

API changes

Data model changes