[Zope] bypass authentication

[u1207440]

I=20made=20a=20signup=20form=20for=20my=20website=20and=20I=20want=20to=20ch=
eck=20if=20the=20username=20already=20exists=20in=20acl_users=20folder=20wit=
hout=20having=20to=20log=20in=20as=20administrator.=20

How=20do=20I=20do=20that,=20what=20and=20where=20do=20I=20have=20to=20modify=
=20my=20permission=20for=20so=20I=20can=20use=20acl_users.getUser(REQUEST.na=
me)=20without=20having=20to=20login=20first??=20(Zope=20tells=20me=20that=20=
I=20don't=20have=20permission=20to=20use=20the=20getUser=20method)