pkce.rb

require 'base64'
require 'openssl'
require 'securerandom'
require 'uri'

BASE_URL = ENV['OAUTH2_BASE_URL']
REDIRECT_URI = ENV['REDIRECT_URI']
CLIENT_ID = ENV['OAUTH2_CLIENT_ID']

code_verifier = Base64.urlsafe_encode64(SecureRandom.bytes(128), padding: false)
code_challenge = Base64.urlsafe_encode64(
  OpenSSL::Digest::SHA256.digest(code_verifier),
  padding: false,
)
state = SecureRandom.uuid

params = {
  client_id: CLIENT_ID,
  response_type: 'code',
  scope: 'openid',
  redirect_uri: REDIRECT_URI,
  state: state,
  code_challenge_method: 'S256',
  code_challenge: code_challenge,
}
param_string = params.map { |k, v| "#{k.to_s}=#{URI.encode_www_form_component(v)}" }.join('&')
puts "#{BASE_URL}/authorize?#{param_string}"
puts code_verifier