public String getServerName() throws Exception {
        Server server = Servers.getInstance().query(this.serverId);
        return server != null ? server.toString() : "";
    }
Get CommonName from SubjectDN.
If regex capture is failed, return inputted SubjectDN.
@param subject: SubjectDN
@return cn or subject
src/main/java/core/packetproxy/model/ClientCertificate.java