Authorization without Authentication?

I have seen this link: http://perl.apache.org/docs/2.0/user/handlers/http.html#PerlAuthzHandler

and as it said: This phase requires a successful authentication from the
previous phase,  because a username is needed in order to decide
whether a user is authorized to access the requested resource.

but what if I don't want to authenticate users (BECAUSE I have already authenticate them using freeRADIUS and IEE802.1x) , I want only to authorize them, you would ask me how can we get the username.

I have usernames with there IPs in mysql DB like this:

user    IP
Mark   192.168.1.10
Mike    192.168.1.11

and I have them too in the DNS:

in its revers zone (1.168.192.in-addr.arpa):

$TTL 60 ; 1 minute 
10            PTR Mark
11            PTR Mike

How can I let module_perl make use of mysql DB or DNS zone to authorize my users using PerlAuthzHandler ?