working on login_redirection module

Hi , i am working on a module to provide redirection of a user on login to the page he was at or perhaps the page he was going to . Which hook should i use to set a variable holding the value of the current page?

Basically what i want is for a non logged in user not to be redirected to the user page, rather , i want him redirected to the page he was at ( or the page he was going to) after he logs in. I know that logintobogggan and customerror, and in fact drupal itself are all supposed to provide this functionality, but they dont , and i need it to work that way today. All i really want to do is set a persistent variable containing the current page, one that contains the page that was current ( the last page) , and one that holds the url of the link that was clicked.

I've been looking at the page building and node building and menu building sections of the handbook, but tragically , they are pretty old, and i think some stuff has changed. Can anyone point me in the right direction?