Drain Hole and Dropbox?

I’m wondering, since you can use Drain Hole with Amazon S3, can you use it with Dropbox? And how would I set that up? If Dropbox requires authentication, wouldn’t it deny access to the WP user that attempts to download it via Drain Hole? And if I provide the public URL, then of course the files would be publicly available… I’m not an advanced user, but advanced enough to try this out. Let me know if you can provide any advice on this. I’d like a Drain Hole-like solution to secure downloads for particular users on my site. WP has a deficiency in securely serving up downloads or uploads or anything, really.