Overview

Allow multiple users to publish to the same blog.

Background

This enables collaborative publishing to a blog on Write.as. It requires a new concept of user permissions tied to:

1. A collection owned by an organization
2. User membership in the organization
3. Membership permissions allowing publishing from the user

Implementation

Reconfigure permission checks to run through a consistent permission system.

User-owned collections: require publishing user to be the same as the collection owner (a user).

Organization-owned collections: require publishing user to be a member of the collection owner (an organization), and have permission to publish to that collection.