openssl s_client -connect some.https.server:443 -showcerts
is a nice command to run when you want to inspect the server's certificates and its certificate chain.
Is there a way to run this command when you are behind a HTTP/HTTPS proxy ?
You can use proxytunnel:
proxytunnel -p yourproxy:8080 -d www.google.com:443 -a 7000
and then you can do this:
openssl s_client -connect localhost:7000 -showcerts
Hope this can help you!