jazcakes on "Using WordPress as a password protected Blog/ Forum"

Hi there.
New'ish to WordPress and love it. I was wondering, a friend has a business website that she wants to create a password protected blog/ forum. By that I mean post interesting posts herself and allow clients of hers to place text posts of their own and only be able to do this using a password she issues. The whole blog would not be visible to anyone unless they use a link from here site that then requires a password to access. Any suggestions on how I go about this?
Many thanks in advance for any suggestions.