What is altname?

In the context of digital certificates, "altname" refers to the Subject Alternative Name (SAN) extension. This extension allows you to specify additional identities for a certificate beyond the common name (CN).

For example, a certificate can have multiple domain names or IP addresses associated with it. This is particularly useful for securing multiple domains with a single SSL/TLS certificate.

Here’s a simple example of how it might look in a certificate configuration:

[ req ]
distinguished_name = req_distinguished_name
req_extensions = v3_req

[ req_distinguished_name ]
CN = example.com

[ v3_req ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = example.com
DNS.2 = www.example.com
DNS.3 = api.example.com

In this example, the certificate is valid for example.com, www.example.com, and api.example.com.