i’m new to flutter and need some helpguidance. As title says, i want to securely(somehow to protect files from others) share files between users within app (e.g. pdf’s, audio).

So main questions are:

1. What service should i use for storage (Cloud Storage, S3 etc.)
2. How can i protect files within app, for example, one user shares file to second user and only these two user must have access to file.