Hello fellow freelancers!
I have FileChucker (by Encodable) installed on our server, along with Magento.
According to Filechucker's website, FileChucker can be configured so that a user must be logged in to have access to the upload form. In this case, users will need to be logged into Magento in order to upload files via FileChucker script.
For specific details, please visit this page: [url removed, login to view] and search for "Can I make FileChucker work with my existing login system?" Their documentation explains how to do this.
Let me know if you have any questions.