When a browser, like Chrome, is validating a web server's certificate, it uses the public key in the certificate's signing authority to verify the certificate's digital signature. In the case of the exhibit, the browser would use the public key in the DigiCert SHA2 Secure Server CA certificate to check the signature of the Arubapedia web server's certificate. This process ensures that the certificate was indeed issued by the claimed Certificate Authority (CA) and has not been tampered with.
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Browser security documentation and SSL/TLS standards that explain the certificate validation process.
Cybersecurity educational resources that cover the principles of public key infrastructure (PKI) and certificate validation.