Final answer:
To add a Subject Alternative Name to a certificate, modify the certificate signing request to include the SAN field. This can be done by editing the OpenSSL configuration file or through a Certificate Authority's web interface during CSR submission.
Step-by-step explanation:
To add a Subject Alternative Name (SAN) to a certificate, you typically need to modify the certificate signing request (CSR). During the CSR generation process, you'll include the SAN field along with the other certificate information. SANs allow you to secure multiple hostnames with a single certificate. Depending on the tool you are using, the method for adding SANs can differ.
For example, if you are using OpenSSL, you can include SANs by editing the openssl.cnf file or by using the -config flag with your command-line request. You might include lines like:[ v3_req ]subjectAltName = DNS.1:example.com, DNS.2:www.example.comIf you are using a web interface provided by a Certificate Authority (CA), there is often a field where you can list SANs when you submit your CSR. Always ensure that you follow the specific instructions provided by your CA or software documentation.