[Zope] Obtaining the name of the authenticated user from within a product's source code

Hi! I'm writing a product and I need to obtain the name of the authenticated user to use it in the source code of the product. I pass the REQUEST parameter to the product's method and I try to use REQUEST['AUTHENTICATED_USER'] inside it but it says that the property doesn't exist (which is true, because I've inspected the REQUEST object and it has all the 'normal' properties (HTTP_USER_AGENT,URL...) but it doesn't have that property). But if I try to access REQUEST['AUTHENTICATED_USER'] from within a DTMLMethod, it works. Why does this happen? Thanks in advance, Igor Leturia