Teams : how to setup file permissioning.

This came as a surprise for me, but now makes complete sense. So even if its a short post it has to be posted.

 All the files shared in a Team Chat are uploaded to OneDrive for Business of the person who uploads the file.

This means even when you are in a Private chat with someone, he / she can go to Files tab and access all the other files uploaded by different people. 

Each of the file uploaded is stored in the Microsoft Teams Chat Files folder in respective person's One drive for Business. 

Of course MS gives you the option to remove or expand the permissions once the files are uploaded.

That is perhaps the biggest reason why most places like Defense, Govt classified Departments, they are advised not to use teams or don't have teams for sharing documents.

The way around that i have found out is to create document library in SharePoint. And then break the permission of this SharePoint library. Then upload the document in this document library while sharing with team members. Yes, these team members will have to be added to the site and the library, but there we have complete control as to what permissions are to be assigned to them.

Use Cases

Like we can provide them read only permissions and that way even if the document is shared with the users they can't make changes to it.

Another use case can be where in we can provide edit permissions to them, but this permission level is assigned only at library level. So they still don't have access to all other documents in the SharePoint site.

But even when you assign read only permissions to users, they can download the files. To block downloading you will need more granular conditional access control. Though i haven't tested it.

Please let me know if you can find any better solution. As far as i have researched all the the tools, be it Slack, Dropbox or skype same issue persists.