Usage

$ ./self-sign example.com \*.example.com  # SNI and wildcard
$ days=825 ./self-sign example.com  # Change expiration
$ check=1 ./self-sign example.com  # Show certificate

Script

OpenSSL 1.1.1 以降が必要なことに留意する。
バージョンの確認は openssl version から。

#!/bin/bash

# Requires OpenSSL 1.1.1 or later

CN=$1
SAN=""
for name in $*; do
  # Note: IP:x.x.x.x is also valid
  SAN="${SAN}DNS:$name,"
done
SAN=${SAN::-1}

days=${days:-36500}  # days=825 ./self-sign ...
check=${check:-0}  # check=1 ./self-sign ...

secret=$CN.key
public=$CN.crt

openssl req -new -subj "/CN=$CN" -addext subjectAltName=$SAN \
  -newkey rsa:2048 -keyout $secret -nodes -x509 -days $days -out $public

# Check certificate
if [ $check != "0" ]; then
  openssl x509 -text -in $public -noout
fi

echo
echo "Secret key file: $secret"
echo "Public key file: $public"

References