[Zope] Change current user

[Juan Garcia Garcia]

Hi,

  i'm developing a site where there are about nine kind of users. When
an user enter to the site, he is an Anonymous User, but i have a button
that its purpose is to change of current user to another that exists in
an acl_users folder. The user must enter the name and password of the 
user he wants to login as.
This is what i don't know to do, i have read a lot of documentation, and
i have tried with the function 'authenticate', but when i show the name
of the current user (AUTHENTICATED_USER.getUserName), it appears always
the user as i login in the Zope Management Interface.
When i was reading documentation, i saw that many people wanted to do this
before, but i wrote the examples and they didn't work for me.
I know that there are products to solve this problem (like LoginManager),
but i prefer to do it without using them.

Can anybody help me?