If you're just looking to add fields and not completely redefine your auth table this is really simple. From the web2py book:
## after auth = Auth(db)
> auth.settings.extra_fields['auth_user']= [
> Field('address'),
> Field('city'),
> Field('zip'),
> Field('phone')]
> ## before auth.define_tables(username=True)
>
>
Those fields will show up on registration and on the edit profile page.
