Decrypt Rails 6.0 beta session cookies

verify_and_decrypt_session_cookie60beta1.rb

# decode rails session
def verify_and_decrypt_session_cookie(session_value, secret_key_base = Rails.application.secret_key_base)
  serializer = ActiveSupport::MessageEncryptor::NullSerializer
  key_generator = ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
  secret = key_generator.generate_key('encrypted cookie', 32)
  sign_secret = key_generator.generate_key("signed encrypted cookie")
  encryptor = ActiveSupport::MessageEncryptor.new(secret, sign_secret, cipher: "aes-256-cbc", serializer: serializer)
  encryptor.decrypt_and_verify(CGI::unescape session_value)
end

# decode signed cookies
def decode_signed_cookies(cookie_original_value = 'ORIGINAL_VALUE_FROM_YOUR_HTTP_PAYLOAD')
  cookie_payload_value = cookie_original_value.split('--').first
  decoded_payload_string = Base64.decode64(cookie_payload_value)
  decoded_payload = JSON.parse(decoded_payload_string)
  encoded_message = decoded_payload['_rails']['message']
  Base64.decode64 encoded_message
end

# sign cookies
def sign_cookies(value)
  cookie_value = URI.unescape(value)
  secret = Rails.application.secret_key_base
  key = OpenSSL::PKCS5.pbkdf2_hmac_sha1(secret, "signed cookie", 1000, 64)
  digest = OpenSSL::HMAC.hexdigest(OpenSSL::Digest.const_get("SHA1").new, key, cookie_value)
end