The CertPrincipalName element specifies the SSL certificate principal name that is required to connect to the server by using SSL. It is an optional child element of the Protocol element (section 18.104.22.168.1.2.4).
If the CertPrincipalName element is not specified, the default value is "msstd:SERVER", where "SERVER" is the value that is specified in the Server element (section 22.214.171.124.126.96.36.199). For example, if "SERVER" is specified as "server.Contoso.com" and CertPrincipalName is left blank with SSL turned on, the default value of CertPrincipalName would be "msstd:server.Contoso.com".
The CertPrincipalName element is returned only when the connection to the server is authenticated with SSL.