Pass "site url " to Ad Tag

I am using Appnexus for buying inventory through their console but i am facing a major issue there. I am not able to pass "Site's Url" to my advertiser's through appnexus. I want a someone who can made a script that is added to the tag to pass the url to my advertisers. I will prefer a canditate with Prior knowledge of appnexus and url passing. When you contact, please mention your previous projects especially belonging to appnexus or any adserver.