“Does a wildcard certificate work for the root domain?” Yes, all types of wildcard certificates have the capability (just in different ways). Learn how to use a wildcard SSL certificate to cover your primary domain and virtually unlimited first-level subdomains.
A Standard Wildcard Certificate Secures the Root Domain
A wildcard SSL certificate secures a single root domain along with virtually all of its first-level subdomains. You’ll use an asterisk (*) as a placeholder in the SSL certificate’s Common Name (CN)