jwt.rb

# https://jwt.io/
#
# 1. Base64 encoding
# 2. JWTs
# 3. 2Learn JWT (WIP)

require 'jwt'
require 'base64'
require 'openssl'

# base64 URL encoded string
# <header>.<payload>.<signature>

def jwt_encode_decode
  # https://tools.ietf.org/html/rfc7519#section-4.1
  payload = {
    aud: 'learn',
    foo: :bar,
    baz: :qux
  }

  key       = 'baz'
  algorithm = 'HS256'

  token = JWT.encode(payload, key, algorithm)

  puts token
  puts '{ "typ": "JWT", "alg": "HS256"  }.{ "foo": "bar" }.<signature>'

  header64, payload64, signature64 = token.split('.')
  
  header_json  = base64url_decode(header64)
  payload_json = base64url_decode(payload64)
  signature    = base64url_decode(signature64)
  
  puts "HEADER: #{header_json}"
  puts "PAYLOAD: #{payload_json}"
  puts "SIGNATURE: #{signature}"
  
  signing_segment = [header64, payload64].join('.')
  
  digest = OpenSSL::HMAC.digest(OpenSSL::Digest.new(algorithm.sub('HS', 'sha')), key, signing_segment)
  
  puts header_json
  puts payload_json
  
  puts signature
  puts digest
end

def base64url_decode(str)
  str += '=' * (4 - str.length.modulo(4))
  Base64.decode64(str.tr('-_', '+/'))
end

# instead of %2B (+) and %2F (/), use shorter - and _
def base64url_encode(str)
  Base64.encode64(str).tr('+/', '-_').gsub(/[\n=]/, '')
end

jwt_encode_decode

#############################################################
# Base64 Encoding
#############################################################
#  Value  Cha 	Value	Char	Value	Char	Value	Char
#  0	  A	16	Q	32	g	48	w
#  1	  B	17	R	33	h	49	x
#  2	  C	18	S	34	i	50	y
#  3	  D	19	T	35	j	51	z
#  4	  E	20	U	36	k	52	0
#  5	  F	21	V	37	l	53	1
#  6	  G	22	W	38	m	54	2
#  7	  H	23	X	39	n	55	3
#  8	  I	24	Y	40	o	56	4
#  9	  J	25	Z	41	p	57	5
#  10	  K	26	a	42	q	58	6
#  11	  L	27	b	43	r	59	7
#  12	  M	28	c	44	s	60	8
#  13	  N	29	d	45	t	61	9
#  14	  O	30	e	46	u	62	+
#  15	  P	31	f	47	v	63	/