How to Check Secure Proxy Certificate

How to find out what certificate our Secure Proxy presented to the browser upon connection?

This is very easy to see using the browser itself. First ensure you do not have any proxy settings configured in the browser. The navigate to https://secure.proxy.domain.name:8443/, press F12 and select the Security tab as indicated on the following screenshots.

A trusted secure proxy certificate will be displayed within ERR_EMPTY_RESPONSE page. Note if you click on the padlock in the browser address bar the certificate will be shown as trusted.

A non trusted secure proxy certificate will be shown with an error ERR_CERT_COMMON_NAME_INVALID.