Customer Portal to view their own account ONLY

Customer Portal to view their own account ONLY

I am looking at the Customer Portal for my application.  I want to be able to allow users to view their record and be able to update it, view their invoice, pay their invoice, upload a file, etc.

My understanding is that the Portal just gives access to areas in your application to those that you invite.  

How are others tackling this issue?  Or is this an issue at all, am I just mistaken?