I am trying to use an HTTPS proxy with authentication via my Chrome Extension. Even though I am using `chrome.webRequest.onBeforeSendHeaders` to setup custom headers, the HTTPS proxy won't work. 

I suspect this is because Chrome sends a CONNECT request automatically to the proxy without raising an event. The proxy checks for custom authentication headers and in case they are not present, refuses to connect. 

Any ideas on how I can listen for the CONNECT request?