How do you check the certificate is valid or not?

To check if a certificate is valid, first verify that it is signed by a trusted Certificate Authority (CA) by checking the CA's signature against the certificate. Next, ensure the certificate has not expired by comparing the current date with its validity period. Additionally, check if the certificate has been revoked by consulting the CA's Certificate Revocation List (CRL) or using the Online Certificate Status Protocol (OCSP). Finally, confirm that the domain name matches the certificate's Common Name (CN) or Subject Alternative Name (SAN).