RFC 2830 also specifies a means for additional names to be set in a certificate. This is done using the subjectAltName field which is an X.509v3 extension of the basic certificate. This field can be used to list aliases for a server, shared names in a load-balancing setup, or any other desired purpose. A wildcard can also be used, to allow a single certificate to match all hostnames within a given domain.
In the openssl.cnf file, the syntax for this extension is