How to execute a function after user has logged in?

I think I would use the check_password filter, which is used in the wp_check_password() function right after a password has been checked and is passed the user’s ID as well as whether the password check succeeded. Look for it in wp-includes/pluggable.php

Thanks a lot filosofo, that did the trick!

What would be the filter that I would use to replace the wp_check_password() function? So I guess the hook right before the function is called? Would it be the authenticate filter? I may be looking at this the wrong way, I’m just trying to figure out how to use my function for checking passwords instead of the normal wordpress.