Common Name
The primary domain name this certificate is issued for
The Common Name (CN) is the most important field in an SSL certificate as it specifies the primary domain name that the certificate is intended to secure. When a browser connects to a website, it checks if the domain in the URL matches the Common Name in the certificate. This field is part of the certificate's Distinguished Name (DN) and appears in the subject field. For example, if you visit https://www.example.com, the certificate's Common Name should be 'www.example.com' or just 'example.com' depending on how the certificate was issued. If there's a mismatch, browsers will display a security warning to users. Modern certificates often use Subject Alternative Names (SAN) to secure multiple domains, but the Common Name remains a critical component for backwards compatibility and primary domain identification.
Common Name mismatches can trigger Cloudflare Error 526 on proxied sites.