Tools for decoding and creating JSON Web Tokens

README.md

JWT tools

create_jwt.sh Reads a JSON payload and creates a JWT, with or without a signature

decode_jwt.sh Reads a JWT from stdin and decodes as human-readable JSON to stdout

create_jwt.sh

#!/bin/bash
# create_jwt.sh (c) NGINX, Inc. [v0.3 10-Jul-2019] Liam Crilly <liam.crilly@nginx.com>
#
# This script accepts a JSON claimset (JWT payload) and creates produces a
# JOSE-signed token to stdout using one of the supported signature algorithms.
#
# CHANGELOG
# v0.1 Initial version (hs256 only)
# v0.2 Added support for various hs signature lengths
# v0.3 Checks for expired exp claims, option to specify exp duration

if [ $# -eq 0 ]; then
	echo "USAGE: ${0##*/} [-exp <mins>] <alg [secret]> <payload>"
	echo " -exp will set or override the exp claim with the specified duration"
	echo " alg may be 'none' or 'hs*'"
	echo " secret will be used for HMAC (hs*) signature"
	echo " payload of '-' will read from stdin"
	exit 1
fi

# Check that jq is installed so we can check/modify the exp claim
#
hash jq 2> /dev/null
if [ $? -ne 0 ]; then
	echo "${0##*/}: ERROR: please install 'jq' for 'exp' payload manipulation"
	exit
fi

# Command line processing
#
VALIDITY_MINS=0
if [ "$1" == "-exp" ]; then
	VALIDITY_MINS=$2
	shift; shift
fi
case $1 in
	"none")
		HEADER='{"alg":"none","typ":"JWT"}'
		PAYLOAD=$2
		shift
		;;

	"hs256"|"hs384"|"hs512")
		LENGTH=`echo $1 | awk -F"hs" '{print $2}'`
		HEADER="{\"alg\":\"HS$LENGTH\",\"typ\":\"JWT\",\"kid\":\"0001\"}"
		SECRET=$2
		shift; shift
		;;

	*)
		echo "${0##*/}: ERROR: unrecognised or unsupported algorithm, $1"
		exit 1
		;;
esac

if [ "$1" == "-" ]; then
	PAYLOAD=$(cat)
else
	PAYLOAD=$1
fi

# Check payload is valid JSON
#
if [ `echo $PAYLOAD | jq -r . 2>&1 | grep -c ^parse` -gt 0 ]; then
	echo "${0##*/}: ERROR: JWT payload is invalid (not JSON)"
	echo $PAYLOAD | jq .
	exit 1
fi

if [ $VALIDITY_MINS -gt 0 ]; then
	# Set/update the exp claim
	EXP_CLAIM=`date -v +${VALIDITY_MINS}M +%s`
	PAYLOAD=`echo $PAYLOAD | jq ".exp = $EXP_CLAIM"`
else
	# Check/warn if exp is in the past
	EXP_CLAIM=`echo $PAYLOAD | jq -r .exp`
	if [ "$EXP_CLAIM" != "null" ] && [ $EXP_CLAIM -lt `date +%s` ]; then
		echo "${0##*/}: WARNING: exp claim is in the past, `date -j -f %s $EXP_CLAIM`" 1>&2
	fi
fi

JWT=`echo -n $HEADER | base64 | tr '+\/' '-_' | tr -d '='`.`echo -n $PAYLOAD | base64 | tr '+\/' '-_' | tr -d '='`

if [ "$LENGTH" != "" ]; then
	SIG=`echo -n $JWT | openssl dgst -binary -sha$LENGTH -hmac $SECRET | base64 | tr '+\/' '-_' | tr -d '='`
fi

echo $JWT.$SIG

decode_jwt.sh

#!/usr/bin/env bash
#
# decode_jwt.sh (c) NGINX, Inc. [v0.5 19-Nov-2018] Liam Crilly <liam.crilly@nginx.com>
#
# This script accepts a JWT on stdin and decodes the header and payload into
# human-readable JSON texts. It does not perform signature validation.
#
# CHANGELOG
# v0.4 [28-Jul-2016] Stable
# v0.5 [19-Nov-2018] Support for multiple JSON-prettifiers, reports on decode failure

if [ $# -gt 0 ]; then
	echo "${0##*/}: reads a JWT from stdin and decodes as human-readable JSON to stdout"
	exit 1
fi

for json_cli in "jq -C ." "python -m json.tool"; do
	hash ${json_cli%% *} 2> /dev/null # Remove chars beyond space
	if [ $? -eq 0 ]; then
		DO_JSON=$json_cli
		break #for
	fi
done
if [ "$DO_JSON" == "" ]; then
	echo "${0##*/}: WARNING: please install 'jq' or 'python' for prettified JSON output"
	DO_JSON=cat
fi

jwt=$(cat)
for section in `echo -n $jwt | cut -f1-2 -d . | tr '.' ' '`; do
	padding="="
	while [ `echo -n "$padding" | wc -c` -lt 4 ]; do
		decoded=`echo -n "${section}$padding" | base64 -D`
		if [ $? -eq 0 ]; then
			# Decoded OK, see if we can prettify the JSON (might need a trailing '}')
			echo $decoded | $DO_JSON 2>&1 | grep -ve ^Ex -e ^parse
			if [ $? -eq 1 ]; then
				echo $decoded} | $DO_JSON 2>&1 | grep -ve ^Ex -e ^parse
			fi
			# Failed to parse JSON, show what's wrong
			if [ $? -eq 1 ]; then
				echo "${0##*/}: ERROR parsing JSON"
				echo $decoded
				echo $decoded} | $DO_JSON
			fi
			break #while
		fi
		padding="${padding}="
	done
done