Script to generate self-signed certificate with optional alt names

ssl_generate.sh

#!/bin/sh

crt_print_conf() {
   CN="$1"
   ALT_NAMES="$2"

   cat <<EOF
[req]
distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no

[v3_req]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
basicConstraints = CA:TRUE
EOF

[ -z "${ALT_NAMES}" ] || echo "subjectAltName = ${ALT_NAMES}"

cat <<EOF

[req_distinguished_name]
CN = ${CN}
EOF

[ -z "${DN_C}"  ] || echo "C  = ${DN_C}"
[ -z "${DN_ST}" ] || echo "ST = ${DN_ST}"
[ -z "${DN_L}"  ] || echo "L  = ${DN_L}"
[ -z "${DN_O}"  ] || echo "O  = ${DN_O}"
[ -z "${DN_OU}" ] || echo "OU = ${DN_OU}"

}

crt_generate() {
  : ${DAYS:=3650}
  : ${BITS:=2048}
 
  CN=$1
  ALT_NAMES=$2

  if [ -e "${CN}.key" ] ; then
     echo "File already exists: ${CN}.key -- Aborting"
     exit 1
  fi

  CFG="${CN}.cnf"

  crt_print_conf "${CN}" "${ALT_NAMES}" > "${CFG}"

  openssl req -x509 \
          -nodes \
          -config "${CFG}" \
          -days ${DAYS} \
          -newkey rsa:${BITS} \
          -keyout ${CN}.key \
          -out ${CN}.crt

  rm "${CFG}"

  openssl x509 -text < ${CN}.crt > ${CN}.about.txt

  echo "

Generated following files:
   ${CN}.crt       -- certificate
   ${CN}.key       -- private key
   ${CN}.about.txt -- certificate info (delete after reviewing)
"
}



if [ -z "$1" ] ; then
   echo "
Usage: $0 hostname <altnames>
       where altnames is an optional comma separated list of alternative names
       For example 'DNS:other.com,DNS:localhost,IP:127.0.0.1'

Environment variables:
       BITS  -- number of bits to use for key           (default: 2048)
       DAYS  -- number of days certificate is valid for (default: 3650)

       DN_C  -- Country code field                      (default: unset)
       DN_ST -- State field                             (default: unset)
       DN_L  -- City field                              (default: unset)
       DN_O  -- Organization field                      (default: unset)
       DN_OU -- Organization Unit field                 (default: unset)
"
   exit 1
fi

#Uncomment and change to defaults you want
#: ${DN_C=AU}
#: ${DN_ST=ACT}
#: ${DN_L=Canberra}
#: ${DN_O='Internet Widgets Ltd.'}

crt_generate $@

with openssl version "OpenSSL 1.1.0g 2 Nov 2017" I had to modify line 19
from
[ -z "${ALT_NAMES}" ] || echo "subjectAltName = ${ALT_NAMES}"
to
[ -z "${ALT_NAMES}" ] || echo "subjectAltName = DNS:${ALT_NAMES}"

otherwise I had the error:
Error Loading extension section v3_req
140525094543808:error:2207507C:X509 V3 routines:v2i_GENERAL_NAME_ex:missing value:../crypto/x509v3/v3_alt.c:496:
140525094543808:error:22098080:X509 V3 routines:X509V3_EXT_nconf:error in extension:../crypto/x509v3/v3_conf.c:47:name=subjectAltName, value=