This change has been deployed. New uploaded form files will have the new Url format and will require HubSpot authentication to access. Existing form files will be migrated to the new authenticated urls over the next couple days.
We are going to change form file upload urls to require HubSpot users authentication for access/download.
New file links will be in the following form: https://api.hubapi.com/filemanager/api/v2/files/123/signed-url-redirect?&portalId=123&filename=example.jpg
We will also change the accessibility of old files. We will update the old file urls on the submissions and contact records. The old, publicly accessible links will cease to work at that time and will return 404 responses.
HubSpot forms handle a lot of different kinds of information, some of which may be private in nature. To foster trust and ensure proper data handling, we will require HubSpot users authentication to access files uploaded via these forms.
This change is happening on October 16, 2019.
If you have any questions, please join the discussion in the community, where our developer support team will be available to answer your questions.
Edit (11/07/2019): An updated changelog entry with new information.