Securing a Domain With or Without "www"
Historically, if you purchase a GlobalSign SSL Certificate to secure "www.domain.com" it will also secure "domain.com". This means that you do not need to purchase two SSL certificates to secure domain variations.
But starting February 27, 2017, this will change. In order for you to secure both domains you need to order certificate for "www.domain.com" and validate it on "domain.com". For the detailed information regarding this change, please go here.