title: Adding a confirmation to has_and_belongs_to_many
body: <p>I've got 2 models; Groups and Users. They're related via has_and_belongs_to_many.</p>
  
  <p>This works perfectly fine so far; However: I'd like to add a user_confirmed to the story. One user adds another user; Therefore the user isn't confirmed yet. That added user can confirm himself later on, setting user_confirmed to '1' for example.</p>
  
  <p>Now; I'm quite sure this is the best approach. I'm not sure on how to create this approach though. Where do I add the <code>user_confirmed</code> column? How do I approach and change it in my application?</p>
  
  <p>Here's the related part of my schema.rb:</p>
  
  <pre><code>  create_table "groups_users", id: false, force: true do |t|
      t.integer "group_id"
      t.integer "user_id"
    end
  
    add_index "groups_users", ["group_id"], name: "index_groups_users_on_group_id"
    add_index "groups_users", ["user_id"], name: "index_groups_users_on_user_id"
  
    create_table "groups", force: true do |t|
      t.string   "name"
      t.integer  "clocktype"
      t.string   "background"
      t.datetime "created_at"
      t.datetime "updated_at"
    end
  
  
    create_table "users", force: true do |t|
      t.string   "first_name"
      t.string   "last_name"
      t.string   "password"
      t.datetime "created_at"
      t.datetime "updated_at"
      t.string   "email",                  default: "", null: false
      t.string   "encrypted_password",     default: "", null: false
      t.string   "reset_password_token"
      t.datetime "reset_password_sent_at"
      t.datetime "remember_created_at"
      t.integer  "sign_in_count",          default: 0
      t.datetime "current_sign_in_at"
      t.datetime "last_sign_in_at"
      t.string   "current_sign_in_ip"
      t.string   "last_sign_in_ip"
      t.string   "avatar_file_name"
      t.string   "avatar_content_type"
      t.integer  "avatar_file_size"
      t.datetime "avatar_updated_at"
    end
  </code></pre>
  
  <p><strong>Please keep in mind that I don't want to confirm the user registration but the relation between user and group</strong></p>