session cookie decrypter for Rails 5.1

with_active_support.rb

require 'cgi'
require 'json'
require 'active_support'

def verify_and_decrypt_session_cookie(cookie, secret_key_base = Rails.application.secrets.secret_key_base)
  cookie = CGI::unescape(cookie)
  salt         = 'encrypted cookie'
  signed_salt  = 'signed encrypted cookie'
  key_generator = ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
  secret = key_generator.generate_key(salt)[0, ActiveSupport::MessageEncryptor.key_len]
  sign_secret = key_generator.generate_key(signed_salt)
  encryptor = ActiveSupport::MessageEncryptor.new(secret, sign_secret)
  encryptor.decrypt_and_verify(cookie)
end

# Usage:
# cookie = "< the value on the right of `_server_session=<this>`"
# verify_and_decrypt_session_cookie(cookie)

How do you handle Rails.application.secrets.secret_key_base being nil in development? (for new rails 5.2)