Get Username providing IP to radius in accounting mode!

Hi, I have a router (NAS) configured to authenticate from a RADIUS server, and then send accounting information to it (i.e. IP frame address). Then the traffic is redirected through a firewall. Is there any way that the firewall can get the accounting information (Specially username) from RADIUS by providing the IP frame address to it? Firewall needs authentication (to know the username to apply policies) but I don't want to authenticate the user for the second time. If this is not possible, Can RADIUS be configured to send the accounting information (Specially username and IP frame address) to a LDAP server so that the firewall can query the LDAP server for the information? Regards,