x509にSANを表示してもらうオプションさん
openssl x509 -noout -ext subjectAltName
んふんふ
$ :| openssl s_client --connect mastodon.zunda.ninja:443 --servername mastodon.zunda.ninja -showcerts 2>/dev/null | openssl x509 -noout -ext subjectAltName
X509v3 Subject Alternative Name:
DNS:mastodon.zunda.ninja