IDEA: Centralized userId

I believe you are making my point for me. While that solution definitely works, it still requires either a) every authentication library to implement the same method/property/export/etc, or b) my library to guess or be configurable to know how to get that info from the selected authentication solution. For CodeIgniter to have a central, standardized location to get/set this still puts none of the burden on the framework for determining the info, but provides a consistent and reliable way for developers to pass the info between each other in the absence of external standards.