[Zope] how to check a user role with data entred by user?

Hi all. I have a question and I hope someone can help me out. I'm new to zope and the all web thing, I'm using zope2. What I did was this, I created a folder in the ZMI and there I created a user folder(acl_users), in the user folder I defined 2 new roles. Now, I have a log in form where the user fills out user name and password, I want to check if the data he entered matches 1 of the roles I defined in the ZMI . I can't find any info or example how to do it, not on the web nor in the documentation. I would appreciate any help on the matter. Tx in advance