Controlling who is able to view a post is a simple task once the system is established. Limiting access to certain users has several advantages, ranging from a design studio distributing artwork among various clients, or a small school arranging to have its students' homework posted online through a cheap and easy solution.
The easiest method to get this system working is to make the receivers of the information subscribers (since they will not be able to post), and the distributors of information authors (since they can only edit their own posts). This system eliminates several headaches for a webmaster by managing who has access to specific posts. The username will be used for identification of who is allowed to view certain posts since it is unique and, for the most part, constant.