When a device like Device A contacts a secure website and receives a certificate chain from the server, the browser's primary task is to validate the web server's certificate to ensure it is trustworthy. Part of this validation includes checking that the certificate contains a DNS Subject Alternative Name (SAN) that matches the domain name of the website being accessed-in this case, arubapedia.arubanetworks.com. This ensures that the certificate was indeed issued to the entity operating the domain and helps prevent man-in-the-middle attacks where an invalid certificate could be presented by an attacker. The DNS SAN check is critical because it directly ties the digital certificate to the domain it secures, confirming the authenticity of the website to the user's browser.