hmac_passwd.sh

#!/bin/sh

set -e

require() {
	if ! command -v "$1" > /dev/null 2>/dev/null ; then
		>&2 echo "$1 utility not found!"
		exit 1
	fi
}

require openssl
require xxd
require tr
require base64
require date

if [ $# -ne 3 ]; then
	>&2 echo "Usage: $0 <hex secret> <username> <duration>"
	>&2 echo "Example: $0 0123456789abcdef test \"2 hours\""
	exit 2
fi

secret="$1"
username="$2"
duration="$3"
prefix="dumbproxy grant token v1"


ts="$(date -d "$duration" +%s)"
hex_ts="$(printf "%016x" "$ts")"

hex_digest="$(\
	(
		echo -n "$prefix"
		echo -n "$username"
		echo -n "$hex_ts" | xxd -r -p
	) | openssl mac -macopt "hexkey:$secret" -digest sha256 HMAC
)"

password="$(\
	(
		echo -n "$hex_ts" | xxd -r -p
		echo -n "$hex_digest" | xxd -r -p
	) | base64 -w 0 | tr '+/' '-_' | tr -d '='
)"

echo "Username: $username"
echo "Password: $password"