Common name usage is different for client certificates than
it is for server certificates. Generally, the common name on a client
certificate is the proper name of the individual requesting a certificate.
In the case of server certificates, the common name must be the
same as your server's DNS host name (or virtual host name, if name-based
virtual hosting is used). Browsers compare the common name in the
server certificate with the host name of the server they are connecting
to. These must match.