SharePoint/Teams/Planner integration issue

[ksod]

Hello, 

I am building a workflow that involves using planner to send tasks out to users. Below is the flow. Ideally this process is meant to be administered through Teams. The 'administrator' uploads the document, assigns it to a group of individual users, and then the document is sent to the user in the form of a planner task instructing them to review, edit, and then mark as complete. 

The kicker, the users are not supposed to see other documents in the SharePoint site. The client wants personnel to be able to view and edit ONLY the documents they are assigned to, meaning that they do not have any level of permissions in the SharePoint site. To implement this, the administrator just manages the access to each document when they upload it to the document library, works fine if the user has a link to the SharePoint site. Since we don't necessarily want them on the SharePoint site, they are sent the task through planner but for some reason cannot access the 'Plan' (likely since they only have access to the item, not the site). I don't know if there is a workaround for this, hoping to get some insight...

New to this, might be missing something very obvious. Thanks! 

Ksod