[development] How to Log in a user

[stuff at trackingsolutions.ca]

Hello,

I am hacking the user.module to integrate better with my hacked version of the 
ecommerce module :).

I would like to automatically redirect the user after creating a new account 
to the next step in the shopping cart. 

I am having problems tracking down the code that will allow my new user to 
login without having to fill in a form and press the login button. I already 
have the user name and password. So I would like to preform the following:

1. Detect if the action came from the shopping cart. I am successfull in this 
by parsing drupal_get_ destination for cart/checkout.

2. I would like to automatically check the user in without their interaction. 
I need help with this one.

3. Automatically redirect the user to the next step in the shopping cart. I 
need some help with this one.

Thanks for your help.