Change domain in Windows Intergrated sign-in

I'm setting up security for a site on our production server.  I work for a city, and we want to use active directory username/password for this.  The city has several different domains for active directory - police has something like "username.pd.ci.cityname.gov", but most people are in a domain that is like 'ascully.central.cityname.gov'.   So CENTRAL domain active directory accounts are the ones we want to use for our security.  However I cannot access this domain, by default Geocortex Essentials is using the police dept. domain. 

Does anyone know how to change this?  Is it an IIS setting, or in a configuration file for Essentials in the wwwroot directory somewhere?

Thanks

Allen