Enforce certificates against a CA signer certificate

Where in the code I can change to enforce the peers certificates against a CA certificate?

My goal is to not only validate the sender host, but if the sender certificate is from the same authority chain of the receiver.

I can try to do it by myself if you tell me in wich part of the code I can change. I think it is at same place you verify the host name of the certificate is from same of the message signer.