Userstamp help

I want to create a user stamp functionality. user stamp would work like
timestamp. columns named ‘created_by’ or ‘modified_by’ would
automatically have the current session user’s id inserted into it.

To do this I need to pass part of the sessions instance variable to each
model that is called from a controller. I don’t want to explicitly pass
it in the save, create, or update method call of the model.

Is this even possible?
How would you go about getting the data from the controller to the