Get and decode access token from token endpoint

get_and_decode_access_token

#!/usr/bin/env bash
set -e
shopt -s inherit_errexit

function die() {
  if [[ -n "${1}" ]]
  then
    >&2 echo "${1}"
  fi
  exit "${2:-1}"
}

function extract_or_die() {
  [[ -n "${1}" ]]  || die "${2}" "${3:-64}"
  echo "${1}"
}

function add_padding() {
  local input
  read -r input
  input=$(extract_or_die "${input}" "argument must be the string to add padding to" "1")
  local len="${#input}"
  local output
  case "$((${len} % 4))" in
    2)
      output="${input}=="
      ;;
    3)
      output="${input}=" 
      ;;
    *)
      output="${input}"
  esac
  echo "${output}"
}

function get_token() {
  local token_endpoint
  token_endpoint=$(extract_or_die "${1}" "1st parameter must be the token endpoint")
  
  local client_id
  client_id=$(extract_or_die "${2}" "2nd parameter must be client_id")
  
  local client_secret
  client_secret=$(extract_or_die "${3}" "3rd parameter must be client_secret")
  
  local username
  username=$(extract_or_die "${4}" "4th parameter must be username")

  local password
  password=$(extract_or_die "${5}" "5th parameter must be password")

  echo -n "$(curl \
        --data "client_id=${client_id}" \
        --data "client_secret=${client_secret}" \
        --data "username=${username}" \
        --data "password=${password}" \
        --data "grant_type=password" \
        --silent \
        "${token_endpoint}"         `# get token from token endpoint` \
      | jq ".access_token"          `# extract access token from response` \
      | sed 's/"\(.*\)"/\1/g'       `# remove quotes from access token` \
      | sed 's/.*\.\(.*\)\..*/\1/g' `# from the access token, extract the payload` \
      | add_padding                 `# add padding if necesary` \
      | base64 --decode             `# decode the payload` \
      | jq .                        `# use jq to print it nicely` \
  )"
}

if [[ "${1}" == "--help" ]]
then
  echo "Usage: get_and_decode_access_token.sh <token-endpoint> <client-id> <client-secret> <username> <password>"
  exit 0
fi
get_token "${@}"