Yes, it is a problem, and there is no easy solution that I’m aware of.
The only way I could suggest to work around this would be to host all images/documents yourself, then put them behind a firewall and require all of your app users to use a VPN. But that would be an awful solution.
There is an outstanding feature request to provide a private storage option. I believe it is something that Glide may be considering, but I have no idea where it might fit in the feature pipeline.