unlang/python "scripting" for gateway and dns servers

I'd like to derive the gateway based on unlang rules from the assigned ip address/mask I store in ldap. In what configuration file would I put the unlang or python code to implement the rule? For DNS servers, i want to use a subset of the username in something like a case/switch statement. Can I use the username in the accept request during the authorization phase? Where would i put this code (preferrably python but could use unlang)? Would I put in the authorize part of the default config file? Thanks