Secure file storage and access

[itay-grudev]

I would really like options for secure file storage and access. Currently files are available on a server publicly if someone knows their 24 character without any kind of authorisation. Realistically that is not what we call secure.

[turt2live]

This sounds like a duplicate of https://github.com/matrix-org/matrix-doc/issues/701