generate_self_signed_cert

#!/bin/bash

########################################
# command line argument helper functions
########################################

# display usage
usage()
{
  echo "
Usage: $0 -s SUBJECT [-d DAYS] HOSTNAME
All options must be specified before HOSTNAME

Defaults:
  SUBJECT=\"/C=GB/L=London/O=IT/CN=\$HOSTNAME\"
  DAYS=3650"
  exit 2
}

# set a variable and exit with error if it already exists
set_variable()
{
  local varname=$1
  shift
  if [ -z "${!varname}" ]; then
    eval "$varname=\"$@\""
  else
    echo "Error: $varname already set"
    usage
  fi
}

# set a variable unless it already exists
set_default()
{
  local varname=$1
  shift
  if [ -z "${!varname}" ]; then
    eval "$varname=\"$@\""
  fi
}

ARG_COUNT=1

# fail if first argument is not an option and there are more than $ARG_COUNT positional arguments
[[ $1 =~ ^-.+ ]] || [[ "$#" == "$ARG_COUNT" ]] || usage

while getopts 's:d:?hv' c
do
  case $c in
    s) set_variable SUBJECT $OPTARG ;;
    d) set_variable DAYS $OPTARG ;;
    v) set -x ;;
    h|?) usage ;; esac
done

shift $((OPTIND-1))

set_variable HOST $1
set_default SUBJECT "/C=GB/L=London/O=IT/CN=$HOST"
set_default DAYS 3650

###################################
# Main script starts here
# Enter unofficial bash strict mode
###################################
set -euo pipefail
IFS=$'\n\t'

openssl req -new -nodes -x509 -subj "$SUBJECT" -days ${DAYS} -keyout "${HOST}.key" -out "${HOST}.crt" -extensions v3_ca