Parse Jwt and update keys / values using jq

jwt.sh

#!/bin/bash

set -e

## Style
RED='\e[31m'
GREEN='\e[32m'
BLUE='\e[34m'
BOLD='\e[1m'
N='\e[0m'

msg(){
    echo -e "${GREEN}[+]${N} $*"
}

info(){
    echo -e "${BLUE}[-]${N} $*"
}

err(){
    echo -e "${RED}[x]${N} $*" >&2
}

dump_jwt(){
    ### Takes the splitted Jwt as argument
    IFS='.' read -ra parts <<< "$1"
    if [ "${#parts[@]}" -ne 3 ];then
        err "Invalid ${BOLD}JWT${N} input"
        exit 1
    fi

    ### Show header
    info "${BOLD}Header${N}: ${BLUE}${parts[0]}${N}"
    echo -n "${parts[0]}" |jq -R '@base64d |fromjson'

    ### Show payload
    info "${BOLD}Payload${N}: ${BLUE}${parts[1]}${N}"
    echo -n "${parts[1]}" |jq -R '@base64d |fromjson'

    ### Show signature for this token
    info "${BOLD}Signature${N}: ${BLUE}${parts[2]}${N}"
}

update_jwt(){
    ### Update the key "$2" with the new value "$3" within the jwt provided in "$1"
    echo -n "$1" |jq \
                 --argjson keys "$2" --argjson values "$3" -Rr \
                 'split(".") |.[0:2] |map(@base64d) |map(fromjson) |
                  map(
                      reduce (range(0; ($keys|length))) as $i
                      (.;
                          if has($keys[$i]) then
                            .[$keys[$i]] = $values[$i]
                          else
                            .
                          end
                      )
                      |@base64 |gsub("="; "") |gsub("-"; "+") |gsub("_"; "/")
                     )
                  |join(".")'
}

show_help(){
    local indent="  "
    echo "usage: ${0} [-h] [--token TOKEN] [-k KEY [KEY ...]] [-v VALUE [VALUE ...]]"
    if [[ "$1" == "error" ]];then
        echo ""
        err "${0}: error: the following argument is required: ${BOLD}-t/--token${N}"
    fi
    echo -e "\nScript to manipulate ${BOLD}jwt${N}\n"
    echo "options:"
    echo "${indent}-h, --help            show this help message and exit"
    echo "${indent}-t TOKEN, --token TOKEN"
    echo "                               jwt token to update"
    echo "${indent}-k KEY [KEY ...], --keys KEY [KEY ...]"
    echo "                               Keys to update on the token"
    echo "${indent}-v VALUE [VALUE ...], --values VALUE [VALUE ...]"
    echo "                               Values to update on the token"
}

keys=()
values=()
token=""
mode=""

## Simple args parsing
for arg in "$@"; do
    case "$arg" in
        -k|--keys) mode="keys" ;;
        -v|--values) mode="values" ;;
        -t|--token) mode="token" ;;
        -h|--help)
            show_help
            exit
            ;;
        *)
            if [[ $mode == "keys" ]]; then
                keys+=("$arg")
            elif [[ $mode == "values" ]]; then
                values+=("$arg")
            elif [[ $mode == "token" ]]; then
                token="$arg"
            fi
            ;;
    esac
done

if [ "${#keys[@]}" -ne "${#values[@]}" ];then
    err "Length of keys and values must be the same"
    exit
elif [ -z "$token" ];then
    show_help "error"
    exit
fi

json_keys=$(jq -nc '$ARGS.positional' --args "${keys[@]}")
json_values=$(jq -nc '$ARGS.positional' --args "${values[@]}")

msg "Original JWT"
dump_jwt "$token"
signature=$(echo "$token" |cut -d '.' -f 2)

if [ "${#keys[@]}" -gt 0 ];then
    new_jwt=$(update_jwt $token "$json_keys" "$json_values")
    new_jwt="$new_jwt.$signature"

    echo ""
    msg "Changed JWT"
    dump_jwt "${new_jwt}"

    echo "$new_jwt"
fi