CDD 6.6 is shipped with CA Rest Pug-in 2.0. Proxy options mentioned in the below link are not available in CA Rest plug-in 2.0.
CDD 6.6 on-Premise and CDD 6.6 SaaS
For CDD on-premise:
1. "Use Proxy" option is available in CA REST plugin 2.1 (available for download under CDD 6.7 product download section)
2. Stop Apache Tomcat Service.
2. Extract the zip file and copy cdd-rest-plugin.war file into the TOMCAT_HOME/webapps folder.
3. Start Apache Tomcat service.
For CDD on-SaaS
1. Click Administration -> Plugins
2. Use "Sync Plug-in" option to update the plugin.
Why Do I Need a Plug-in Proxy?