Decrypts a Rails (Devise/Warden) cookie in ruby

decrypt_devise_cookie.rb

def decrypt_cookie(cookie, app_secret)
  token_hashed = OpenSSL::PKCS5.pbkdf2_hmac_sha1(app_secret, 'encrypted cookie', 1000, 32)
  encrypted_message = Base64.decode64(cookie).split('--')[0]
  decoded_cookie = Base64.strict_decode64(encrypted_message)
  cipher = OpenSSL::Cipher.new('aes-256-cbc')
  cipher.key = token_hashed
  decrypted_data = cipher.update(decoded_cookie)
  decrypted_data
end