What is a Common Name (CN)?
When generating an SSL certificate, you will be asked to provide the "Common Name" or CN. The common name is the domain name or URL address of the website you want to secure with the certificate.
If you're creating a One Address certificate, filling in the common name is relatively simple: it's the only address you want to secure. Don't forget to specify the subdomain if your URL is based on a subdomain (shop.example.com).
Note
When you create an SSL certificate for an address, if you create the CSR for the Apex domain (example.com), the subdomain "www" will automatically be included by the Certificate Authority. This means that a certificate created for "example.com" will secure both https://example.com and https://www.example.com. The reverse is also true (if you create the CSR for www.example.com, example.com will also be protected). This rule does not apply to other subdomains.
If you're creating a Multi-domain certificate, you only need to include the main address you want to protect in the CSR. This will be the only address you cannot change. You can add additional addresses directly from the Gandi interface, below the CSR field.
Note
Unlike single-address certificates, multi-domain certificates do not protect the "www" sub-domain of an apex address that you have specified. You need to declare each address you want to secure separately. In other words, if you purchase a multi-domain certificate for "example.com", you'll need to specify the address "www.example.com" in the "Subject Alternative Name (SAN)" (additional addresses), as it won't be protected by default as with a One Address certificate.
If you're creating a Wildcard SSL certificate, you'll need to specify a wildcard character, "*", as a subdomain to indicate that you want to secure an entire subdomain level. For example, "*.example.com" will secure any subdomain placed just before the apex domain, such as blog.example.com, but will not include lower-level subdomains like "blog.store.example.com".
Note
Wildcard certificates also secure the apex domain specified in the SSL, in addition to all subdomains at the same level.