Generate expiring activator token or a key hash in rails manually - ruby

Question

I'm trying to verify a link that will expire in a week. I have an activator_token stored in the database, which will be used to generate the link in this format: http://www.example.com/activator_token. (And not activation tokens generated by Devise or Authlogic.)
Is there a way to make this activator token expire (in a week or so) without comparing with updated_at or some other date. Something like an encoded token, which will return nil when decoded after a week. Can any existing modules in Ruby do this? I don't want to store the generated date in the database or in an external store like Redis and compare it with Time.now. I want it to be very simple, and wanted to know if something like this already exists, before writing the logic again.

Answer 1

What you want to use is: https://github.com/jwt/ruby-jwt .
Here is some boilerplate code so you can try it out yourself.
require 'jwt'
# generate your keys when deploying your app.
# Doing so using a rake task might be a good idea
# How to persist and load the keys is up to you!
rsa_private = OpenSSL::PKey::RSA.generate 2048
rsa_public = rsa_private.public_key
# do this when you are about to send the email
exp = Time.now.to_i + 4 * 3600
payload = {exp: exp, discount: '9.99', email: 'user#example.com'}
# when generating an invite email, this is the token you want to incorporate in
# your link as a parameter
token = JWT.encode payload, rsa_private, 'RS256'
puts token
puts token.length
# this goes into your controller
begin
#token = params[:token]
decoded_token = JWT.decode token, rsa_public, true, { :algorithm => 'RS256' }
puts decoded_token.first
# continue with your business logic
rescue JWT::ExpiredSignature
# Handle expired token
# inform the user his invite link has expired!
puts "Token expired"
end