title: Using devise_invitable for adding Users to a Group in Ruby on Rails?
body: <p>I have a "Groups" resource within my app that Users can join (a Group has_and_belongs_to_many Users and vice versa). The <a href="https://github.com/scambra/devise_invitable" rel="noreferrer">devise_invitable</a> plugin allows an existing User on my app to email an invitation to another poetntial User to register on the site, but I want some extra functionality: I want a User to be able to <em>invite someone to a particular Group</em>, so that as soon as they accept that invitation in the email, they can see a link to join that Group.</p>
  
  <p>Has anyone used devise_invitable to do something like this? What's the best way to go about adding this extra functionality? It seems I'd need to include some sort of of "Group token" identifying the Group in the invite email, then pass it back in the URL that the user clicks to accept the invite.</p>
  
  <p>Should I be overriding the invitations controller methods, or is there another plugin that serves the purpose better?</p>