adds omniauth basic authentication process with Twitter, including an intermediate step to ask the user for her email if not provided by the OAuth provider - Twitter, for instance

app/controllers/application_controller.rb

@@ -13,6 +13,8 @@ class ApplicationController < ActionController::Base
   # For APIs, you may want to use :null_session instead.
   protect_from_forgery with: :exception
 
+  before_action :ensure_signup_complete
+
   rescue_from CanCan::AccessDenied do |exception|
     redirect_to main_app.root_url, alert: exception.message
   end
@@ -40,4 +42,13 @@ class ApplicationController < ActionController::Base
     def set_debate_votes(debates)
       @voted_values = current_user ? current_user.debate_votes(debates) : {}
     end
+
+    def ensure_signup_complete
+      # Ensure we don't go into an infinite loop
+      return if action_name.in? %w(finish_signup do_finish_signup)
+
+      if user_signed_in? && !current_user.email_provided?
+        redirect_to finish_signup_path
+      end
+    end
 end

app/controllers/users/omniauth_callbacks_controller.rb

@@ -0,0 +1,30 @@
+class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
+  def self.provides_callback_for(provider)
+    class_eval %Q{
+      def #{provider}
+        @user = User.find_for_oauth(env["omniauth.auth"], current_user)
+
+        if @user.persisted?
+          sign_in_and_redirect @user, event: :authentication
+          set_flash_message(:notice, :success, kind: "#{provider}".capitalize) if is_navigational_format?
+        else
+          session["devise.#{provider}_data"] = env["omniauth.auth"]
+          redirect_to new_user_registration_url
+        end
+      end
+    }
+  end
+
+  # [:twitter, :facebook, :google_oauth2].each do |provider|
+  [:twitter].each do |provider|
+    provides_callback_for provider
+  end
+
+  def after_sign_in_path_for(resource)
+    if resource.email_provided?
+      super(resource)
+    else
+      finish_signup_path
+    end
+  end
+end

app/controllers/users/registrations_controller.rb

@@ -1,4 +1,5 @@
 class Users::RegistrationsController < Devise::RegistrationsController
+  prepend_before_filter :authenticate_scope!, only: [:edit, :update, :destroy, :finish_signup, :do_finish_signup]
 
   def create
     build_resource(sign_up_params)
@@ -9,6 +10,20 @@ class Users::RegistrationsController < Devise::RegistrationsController
     end
   end
 
+  def finish_signup
+  end
+
+  def do_finish_signup
+    if current_user.update(sign_up_params)
+      current_user.skip_reconfirmation!
+      sign_in(current_user, bypass: true)
+      redirect_to root_url, notice: I18n.t('devise.registrations.updated')
+    else
+      @show_errors = true
+      render :finish_signup
+    end
+  end
+
   private
 
     def sign_up_params

app/models/user.rb

@@ -1,8 +1,12 @@
 class User < ActiveRecord::Base
   include ActsAsParanoidAliases
+
+  OMNIAUTH_EMAIL_PREFIX = 'omniauth@participacion'
+  OMNIAUTH_EMAIL_REGEX  = /\A#{OMNIAUTH_EMAIL_PREFIX}/
+
   apply_simple_captcha
   devise :database_authenticatable, :registerable, :confirmable,
-         :recoverable, :rememberable, :trackable, :validatable
+         :recoverable, :rememberable, :trackable, :validatable, :omniauthable
 
   acts_as_voter
   acts_as_paranoid column: :hidden_at
@@ -11,9 +15,11 @@ class User < ActiveRecord::Base
   has_one :moderator
   has_one :organization
   has_many :inappropiate_flags
+  has_many :identities, dependent: :destroy
 
-  validates :username,   presence: true, unless: :organization?
+  validates :username, presence: true, unless: :organization?
   validates :official_level, inclusion: {in: 0..5}
+  validates_format_of :email, without: OMNIAUTH_EMAIL_REGEX, on: :update
 
   validates_associated :organization, message: false
 
@@ -25,6 +31,47 @@ class User < ActiveRecord::Base
   scope :organizations,  -> { joins(:organization) }
   scope :officials,      -> { where("official_level > 0") }
 
+  def self.find_for_oauth(auth, signed_in_resource = nil)
+    # Get the identity and user if they exist
+    identity = Identity.find_for_oauth(auth)
+
+    # If a signed_in_resource is provided it always overrides the existing user
+    # to prevent the identity being locked with accidentally created accounts.
+    # Note that this may leave zombie accounts (with no associated identity) which
+    # can be cleaned up at a later date.
+    user = signed_in_resource ? signed_in_resource : identity.user
+
+    # Create the user if needed
+    if user.nil?
+
+      # Get the existing user by email if the provider gives us a verified email.
+      # If no verified email was provided we assign a temporary email and ask the
+      # user to verify it on the next step via RegistrationsController.finish_signup
+      email_is_verified = auth.info.email && (auth.info.verified || auth.info.verified_email)
+      email = auth.info.email if email_is_verified
+      user = User.where(email: email).first if email
+
+      # Create the user if it's a new registration
+      if user.nil?
+        user = User.new(
+          username: auth.info.nickname || auth.extra.raw_info.name.parameterize('-') || auth.uid,
+          email: email ? email : "#{OMNIAUTH_EMAIL_PREFIX}-#{auth.uid}-#{auth.provider}.com",
+          password: Devise.friendly_token[0,20]
+        )
+        user.skip_confirmation!
+        user.save!
+      end
+    end
+
+    # Associate the identity with the user if needed
+    if identity.user != user
+      identity.user = user
+      identity.save!
+    end
+
+    user
+  end
+
   def name
     organization? ? organization.name : username
   end
@@ -67,4 +114,8 @@ class User < ActiveRecord::Base
     e.present? ? where(email: e) : none
   end
 
+  def email_provided?
+    !!(email && email !~ OMNIAUTH_EMAIL_REGEX) ||
+      !!(unconfirmed_email && unconfirmed_email !~ OMNIAUTH_EMAIL_REGEX)
+  end
 end

app/views/devise/_omniauth_form.html.erb

@@ -0,0 +1,5 @@
+<br/>
+
+<%= link_to t("omniauth.twitter.sign_in"), user_omniauth_authorize_path(:twitter), class: 'button radius expand' %>
+
+<hr/>

app/views/devise/menu/_login_items.html.erb

@@ -7,11 +7,11 @@
       <%= link_to(t("devise_views.menu.login_items.logout"), destroy_user_session_path, method: :delete) %>
     </li>
   <% else %>
-  <li>
-    <%= link_to(t("devise_views.menu.login_items.login"), new_user_session_path)  %>
-  </li>
-  <li>
-    <%= link_to(t("devise_views.menu.login_items.signup"), new_user_registration_path, class: "button radius small") %>
-  </li>
+    <li>
+      <%= link_to(t("devise_views.menu.login_items.login"), new_user_session_path)  %>
+    </li>
+    <li>
+      <%= link_to(t("devise_views.menu.login_items.signup"), new_user_registration_path, class: "button radius small") %>
+    </li>
   <% end %>
 </ul>

app/views/devise/sessions/new.html.erb

@@ -3,6 +3,8 @@
     <div class="panel">
       <h2><%= t("devise_views.sessions.new.title") %></h2>
 
+      <%= render 'devise/omniauth_form' %>
+
       <%= form_for(resource, as: resource_name, url: session_path(resource_name)) do |f| %>
         <div class="row">
           <div class="small-12 columns">

app/views/users/registrations/finish_signup.html.erb

@@ -0,0 +1,13 @@
+<div class="auth row">
+  <div class="small-12 medium-8 large-5 column small-centered">
+    <div class="panel">
+      <h1><%= t('omniauth.finish_signup.title') %></h1>
+
+      <%= form_for current_user, as: :user, url: do_finish_signup_path, html: { role: 'form'} do |f| %>
+        <%= render 'shared/errors', resource: current_user %>
+        <%= f.email_field :email, placeholder: t("devise_views.users.registrations.new.email_label"), value: nil %>
+        <%= f.submit t("devise_views.users.registrations.new.submit"), class: 'button radius' %>
+      <% end %>
+    </div>
+  </div>
+</div>

app/views/users/registrations/new.html.erb

@@ -2,6 +2,9 @@
   <div class="small-12 medium-8 large-5 column small-centered">
     <div class="panel">
       <h2><%= t("devise_views.users.registrations.new.title") %></h2>
+
+      <%= render 'devise/omniauth_form' %>
+
       <%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
         <%= render 'shared/errors', resource: resource %>
 

config/initializers/devise.rb

@@ -239,6 +239,7 @@ Devise.setup do |config|
   # Add a new OmniAuth provider. Check the wiki for more information on setting
   # up on your models and hooks.
   # config.omniauth :github, 'APP_ID', 'APP_SECRET', scope: 'user,public_repo'
+  config.omniauth :twitter, Rails.application.secrets.twitter_key, Rails.application.secrets.twitter_secret
 
   # ==> Warden configuration
   # If you want to use other strategies, that are not supported by Devise, or

config/initializers/omniauth.rb

@@ -1,4 +0,0 @@
-Rails.application.config.middleware.use OmniAuth::Builder do
-  provider :developer unless Rails.env.production?
-  provider :twitter, Rails.application.secrets.twitter_key, Rails.application.secrets.twitter_secret
-end

config/locales/en.yml

@@ -148,3 +148,9 @@ en:
       all: "You are not authorized to %{action} %{subject}."
   welcome:
     last_debates: Last debates
+  omniauth:
+    finish_signup:
+      title: Add Email
+    twitter:
+      sign_in: Sign in with Twitter
+    or: or

config/locales/es.yml

@@ -148,3 +148,9 @@ es:
       all: "No tienes permiso para realizar la acción '%{action}' sobre %{subject}."
   welcome:
     last_debates: Últimos debates
+  omniauth:
+    finish_signup:
+      title: Añade tu email
+    twitter:
+      sign_in: Inicia sessión con Twitter
+    or: o

config/routes.rb

@@ -1,10 +1,19 @@
 Rails.application.routes.draw do
-  devise_for :users, controllers: { registrations: 'users/registrations' }
+  devise_for :users, controllers: {
+                       registrations: 'users/registrations',
+                       omniauth_callbacks: 'users/omniauth_callbacks'
+                     }
   devise_for :organizations, class_name: 'User',
              controllers: {
                registrations: 'organizations/registrations',
-               sessions: 'devise/sessions'
-             }
+               sessions: 'devise/sessions',
+             },
+             skip: [:omniauth_callbacks]
+
+  devise_scope :user do
+    get :finish_signup, to: 'users/registrations#finish_signup'
+    patch :do_finish_signup, to: 'users/registrations#do_finish_signup'
+  end
 
   # The priority is based upon order of creation: first created -> highest priority.
   # See how all your routes lay out with "rake routes".