diff --git a/Gemfile b/Gemfile
index e2b104de0..14029a3c9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -21,6 +21,11 @@ gem 'turbolinks'
 gem 'devise'
 # Use ActiveModel has_secure_password
 # gem 'bcrypt', '~> 3.1.7'
+gem 'omniauth'
+gem 'omniauth-twitter'
+gem 'omniauth-facebook'
+gem 'omniauth-google-oauth2'
+
 gem 'kaminari'
 gem 'acts_as_commentable_with_threading'
 gem 'acts-as-taggable-on'
diff --git a/Gemfile.lock b/Gemfile.lock
index 67d007883..adeb5d99f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -133,6 +133,8 @@ GEM
     factory_girl_rails (4.5.0)
       factory_girl (~> 4.5.0)
       railties (>= 3.0.0)
+    faraday (0.9.1)
+      multipart-post (>= 1.2, < 3)
     foundation-rails (5.5.2.1)
       railties (>= 3.1.0)
       sass (>= 3.3.0, < 3.5)
@@ -150,6 +152,7 @@ GEM
       activesupport (>= 4.1.0)
     groupdate (2.4.0)
       activesupport (>= 3)
+    hashie (3.4.2)
     highline (1.7.3)
     http-cookie (1.0.2)
       domain_name (~> 0.5)
@@ -169,6 +172,7 @@ GEM
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
     json (1.8.3)
+    jwt (1.5.1)
     kaminari (0.16.3)
       actionpack (>= 3.0.0)
       activesupport (>= 3.0.0)
@@ -189,12 +193,38 @@ GEM
     mini_portile (0.6.2)
     minitest (5.8.0)
     multi_json (1.11.2)
+    multi_xml (0.5.5)
+    multipart-post (2.0.0)
     net-scp (1.2.1)
       net-ssh (>= 2.6.5)
     net-ssh (2.9.2)
     netrc (0.10.3)
     nokogiri (1.6.6.2)
       mini_portile (~> 0.6.0)
+    oauth (0.4.7)
+    oauth2 (1.0.0)
+      faraday (>= 0.8, < 0.10)
+      jwt (~> 1.0)
+      multi_json (~> 1.3)
+      multi_xml (~> 0.5)
+      rack (~> 1.2)
+    omniauth (1.2.2)
+      hashie (>= 1.2, < 4)
+      rack (~> 1.0)
+    omniauth-facebook (2.0.1)
+      omniauth-oauth2 (~> 1.2)
+    omniauth-google-oauth2 (0.2.6)
+      omniauth (> 1.0)
+      omniauth-oauth2 (~> 1.1)
+    omniauth-oauth (1.1.0)
+      oauth
+      omniauth (~> 1.0)
+    omniauth-oauth2 (1.3.1)
+      oauth2 (~> 1.0)
+      omniauth (~> 1.2)
+    omniauth-twitter (1.2.1)
+      json (~> 1.3)
+      omniauth-oauth (~> 1.1)
     orm_adapter (0.5.0)
     paranoia (2.1.3)
       activerecord (~> 4.0)
@@ -362,6 +392,10 @@ DEPENDENCIES
   kaminari
   launchy
   letter_opener_web (~> 1.3.0)
+  omniauth
+  omniauth-facebook
+  omniauth-google-oauth2
+  omniauth-twitter
   paranoia
   pg
   poltergeist
diff --git a/README.md b/README.md
index 6c8bbb453..87e0d1ab9 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ Para ejecutar la aplicación en local:
 bundle exec bin/rails s
 ```
 
-Prerequisitos para los tests: tener instalado PhantomJS >= 2.0 
+Prerequisitos para los tests: tener instalado PhantomJS >= 2.0
 
 Para ejecutar los tests:
 
@@ -44,6 +44,12 @@ Para ejecutar los tests:
 bundle exec bin/rspec
 ```
 
+### OAuth
+
+Para probar los servicios de autenticación mediante proveedores externos OAuth — en este momento Twitter, Facebook y Google —, necesitas crear una "aplicación" en cada una de las plataformas soportadas y configurar la *key* y el *secret* proporcionados en tu *secrets.yml*
+
+En el caso de Google, comprueba que las APIs *Contacts API* y *Google+ API* están habilitadas para la aplicación.
+
 ## Licencia
 
 El código de este proyecto está publicado bajo la licencia AFFERO GPL v3 (ver [LICENSE-AGPLv3.txt](LICENSE-AGPLv3.txt))
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index b879a4a8d..802dda3bc 100644
--- a/app/controllers/application_controller.rb
+++ b/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
diff --git a/app/controllers/users/omniauth_callbacks_controller.rb b/app/controllers/users/omniauth_callbacks_controller.rb
new file mode 100644
index 000000000..8588ba243
--- /dev/null
+++ b/app/controllers/users/omniauth_callbacks_controller.rb
@@ -0,0 +1,29 @@
+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|
+    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
diff --git a/app/controllers/users/registrations_controller.rb b/app/controllers/users/registrations_controller.rb
index 0ef0ba638..4ce5998c8 100644
--- a/app/controllers/users/registrations_controller.rb
+++ b/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 +10,19 @@ 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
+    else
+      render :finish_signup
+    end
+  end
+
   private
 
     def sign_up_params
diff --git a/app/models/identity.rb b/app/models/identity.rb
new file mode 100644
index 000000000..3ba19e3fa
--- /dev/null
+++ b/app/models/identity.rb
@@ -0,0 +1,17 @@
+class Identity < ActiveRecord::Base
+  belongs_to :user
+
+  validates :provider, presence: true
+  validates :uid, presence: true, uniqueness: { scope: :provider }
+
+  def self.find_for_oauth(auth)
+    where(uid: auth.uid, provider: auth.provider).first_or_create
+  end
+
+  def update_user(new_user)
+    return unless user != new_user
+
+    self.user = new_user
+    save!
+  end
+end
diff --git a/app/models/user.rb b/app/models/user.rb
index 544142c2f..7cff8d732 100644
--- a/app/models/user.rb
+++ b/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 +31,43 @@ 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
+    user ||= first_or_create_for_oauth(auth)
+
+    # Associate the identity with the user if needed
+    identity.update_user(user)
+    user
+  end
+
+  # 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
+  def self.first_or_create_for_oauth(auth)
+    email = auth.info.email if auth.info.verified || auth.info.verified_email
+    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
+
+    user
+  end
+
   def name
     organization? ? organization.name : username
   end
@@ -67,4 +110,8 @@ 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
diff --git a/app/views/devise/_omniauth_form.html.erb b/app/views/devise/_omniauth_form.html.erb
new file mode 100644
index 000000000..fdd812b4f
--- /dev/null
+++ b/app/views/devise/_omniauth_form.html.erb
@@ -0,0 +1,7 @@
+<br/>
+
+<%= link_to t("omniauth.twitter.sign_in"), user_omniauth_authorize_path(:twitter), class: 'button radius expand' %>
+<%= link_to t("omniauth.facebook.sign_in"), user_omniauth_authorize_path(:facebook), class: 'button radius expand' %>
+<%= link_to t("omniauth.google_oauth2.sign_in"), user_omniauth_authorize_path(:google_oauth2), class: 'button radius expand' %>
+
+<hr/>
diff --git a/app/views/devise/menu/_login_items.html.erb b/app/views/devise/menu/_login_items.html.erb
index 4959553f9..6cd27160d 100644
--- a/app/views/devise/menu/_login_items.html.erb
+++ b/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>
\ No newline at end of file
+</ul>
diff --git a/app/views/devise/passwords/new.html.erb b/app/views/devise/passwords/new.html.erb
index 78a8b8b4c..1219c393d 100644
--- a/app/views/devise/passwords/new.html.erb
+++ b/app/views/devise/passwords/new.html.erb
@@ -19,4 +19,4 @@
       <%= render "devise/shared/links" %>
     </div>
   </div>
-</div>
\ No newline at end of file
+</div>
diff --git a/app/views/devise/sessions/new.html.erb b/app/views/devise/sessions/new.html.erb
index 391ef186c..ab0b22426 100644
--- a/app/views/devise/sessions/new.html.erb
+++ b/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">
@@ -28,4 +30,4 @@
       <%= render "devise/shared/links" %>
     </div>
   </div>
-</div>
\ No newline at end of file
+</div>
diff --git a/app/views/devise/shared/_links.html.erb b/app/views/devise/shared/_links.html.erb
index 0fd80f429..7f8142144 100644
--- a/app/views/devise/shared/_links.html.erb
+++ b/app/views/devise/shared/_links.html.erb
@@ -25,7 +25,7 @@
 	  <%= link_to t("devise_views.shared.links.new_unlock"), new_unlock_path(resource_name) %><br>
 	<% end -%>
 
-	<%- if devise_mapping.omniauthable? %>
+	<%- if devise_mapping.omniauthable? && devise_mapping.name == 'user' %>
 	  <%- resource_class.omniauth_providers.each do |provider| %>
 	    <%= link_to t("devise_views.shared.links.signin_with_provider", provider: provider.to_s.titleize), omniauth_authorize_path(resource_name, provider) %><br>
 	  <% end -%>
diff --git a/app/views/users/registrations/finish_signup.html.erb b/app/views/users/registrations/finish_signup.html.erb
new file mode 100644
index 000000000..c57f01a8e
--- /dev/null
+++ b/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>
diff --git a/app/views/users/registrations/new.html.erb b/app/views/users/registrations/new.html.erb
index 92344b76f..2ac5b7af6 100644
--- a/app/views/users/registrations/new.html.erb
+++ b/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 %>
 
diff --git a/config/deploy/shared/secrets.yml.erb b/config/deploy/shared/secrets.yml.erb
index a1cc29fb8..42a8c48a6 100644
--- a/config/deploy/shared/secrets.yml.erb
+++ b/config/deploy/shared/secrets.yml.erb
@@ -2,4 +2,10 @@
   recaptcha_public_key: <%= ENV["MADRID_RECAPTCHA_PUBLIC_KEY"] %>
   recaptcha_private_key: <%= ENV["MADRID_RECAPTCHA_PRIVATE_KEY"] %>
   secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
-  server_name: <%= fetch(:server_name) %>
\ No newline at end of file
+  twitter_key: <%= ENV["TWITTER_KEY"] %>
+  twitter_secret: <%= ENV["TWITTER_SECRET"] %>
+  facebook_key: <%= ENV["FACEBOOK_KEY"] %>
+  facebook_secret: <%= ENV["FACEBOOK_SECRET"] %>
+  google_oauth2_key: <%= ENV["GOOGLE_KEY"] %>
+  google_oauth2_secret: <%= ENV["GOOGLE_SECRET"] %>
+  server_name: <%= fetch(:server_name) %>
diff --git a/config/initializers/devise.rb b/config/initializers/devise.rb
index f7cdfb292..40f3e50b3 100644
--- a/config/initializers/devise.rb
+++ b/config/initializers/devise.rb
@@ -239,6 +239,9 @@ 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
+  config.omniauth :facebook, Rails.application.secrets.facebook_key, Rails.application.secrets.facebook_secret
+  config.omniauth :google_oauth2, Rails.application.secrets.google_oauth2_key, Rails.application.secrets.google_oauth2_secret
 
   # ==> Warden configuration
   # If you want to use other strategies, that are not supported by Devise, or
diff --git a/config/locales/devise.es.yml b/config/locales/devise.es.yml
index f39099f57..c2bc246e9 100644
--- a/config/locales/devise.es.yml
+++ b/config/locales/devise.es.yml
@@ -55,4 +55,4 @@ es:
       not_locked: "no estaba bloqueado."
       not_saved:
         one: "1 error impidió que este %{resource} fuera guardado:"
-        other: "%{count} errores impidieron que este %{resource} fuera guardado:"
\ No newline at end of file
+        other: "%{count} errores impidieron que este %{resource} fuera guardado:"
diff --git a/config/locales/en.yml b/config/locales/en.yml
index ce3339b25..279b2a00e 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -148,3 +148,12 @@ 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
+    facebook:
+      sign_in: Sign in with Facebook
+    google_oauth2:
+      sign_in: Sign in with Google
diff --git a/config/locales/es.yml b/config/locales/es.yml
index 1e2cca785..98c463b1e 100644
--- a/config/locales/es.yml
+++ b/config/locales/es.yml
@@ -148,3 +148,12 @@ 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: Entra con Twitter
+    facebook:
+      sign_in: Entra con Facebook
+    google_oauth2:
+      sign_in: Entra con Google
diff --git a/config/routes.rb b/config/routes.rb
index f224609b9..a51c75c39 100644
--- a/config/routes.rb
+++ b/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".
diff --git a/config/secrets.yml.example b/config/secrets.yml.example
index f4ad98027..1d1312ea6 100644
--- a/config/secrets.yml.example
+++ b/config/secrets.yml.example
@@ -14,12 +14,30 @@ default: &default
 
 development:
   secret_key_base: 56792feef405a59b18ea7db57b4777e855103882b926413d4afdfb8c0ea8aa86ea6649da4e729c5f5ae324c0ab9338f789174cf48c544173bc18fdc3b14262e4
+  twitter_key: AAAA
+  twitter_secret: BBBB
+  facebook_key: AAAA
+  facebook_secret: BBBB
+  google_oauth2_key: AAAA
+  google_oauth2_secret: BBBB
   <<: *default
 
 test:
   secret_key_base: 4d5adf961ddd27aef19622d6c0b3234d555f9ee003f022b1f829c92bbe33aaee907be7feb67bd54c14a1a32512fa968565ad405971fbc41bd0797af73c26a796
+  twitter_key: AAAA
+  twitter_secret: BBBB
+  facebook_key: AAAA
+  facebook_secret: BBBB
+  google_oauth2_key: AAAA
+  google_oauth2_secret: BBBB
   <<: *default
 
 production:
   secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
-  <<: *default
\ No newline at end of file
+  twitter_key: <%= ENV["TWITTER_KEY"] %>
+  twitter_secret: <%= ENV["TWITTER_SECRET"] %>
+  facebook_key: <%= ENV["FACEBOOK_KEY"] %>
+  facebook_secret: <%= ENV["FACEBOOK_SECRET"] %>
+  google_oauth2_key: <%= ENV["GOOGLE_KEY"] %>
+  google_oauth2_secret: <%= ENV["GOOGLE_SECRET"] %>
+  <<: *default
diff --git a/db/migrate/20150824144524_create_identities.rb b/db/migrate/20150824144524_create_identities.rb
new file mode 100644
index 000000000..38a5e603a
--- /dev/null
+++ b/db/migrate/20150824144524_create_identities.rb
@@ -0,0 +1,11 @@
+class CreateIdentities < ActiveRecord::Migration
+  def change
+    create_table :identities do |t|
+      t.references :user, index: true, foreign_key: true
+      t.string :provider
+      t.string :uid
+
+      t.timestamps null: false
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 12e457a1c..d21459719 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20150824113326) do
+ActiveRecord::Schema.define(version: 20150824144524) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -66,8 +66,8 @@ ActiveRecord::Schema.define(version: 20150824113326) do
     t.integer  "author_id"
     t.datetime "created_at",                                        null: false
     t.datetime "updated_at",                                        null: false
-    t.datetime "hidden_at"
     t.string   "visit_id"
+    t.datetime "hidden_at"
     t.datetime "flagged_as_inappropiate_at"
     t.integer  "inappropiate_flags_count",              default: 0
     t.datetime "reviewed_at"
@@ -75,6 +75,16 @@ ActiveRecord::Schema.define(version: 20150824113326) do
 
   add_index "debates", ["hidden_at"], name: "index_debates_on_hidden_at", using: :btree
 
+  create_table "identities", force: :cascade do |t|
+    t.integer  "user_id"
+    t.string   "provider"
+    t.string   "uid"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+  end
+
+  add_index "identities", ["user_id"], name: "index_identities_on_user_id", using: :btree
+
   create_table "inappropiate_flags", force: :cascade do |t|
     t.integer  "user_id"
     t.string   "flaggable_type"
@@ -156,10 +166,10 @@ ActiveRecord::Schema.define(version: 20150824113326) do
     t.string   "unconfirmed_email"
     t.boolean  "email_on_debate_comment",            default: false
     t.boolean  "email_on_comment_reply",             default: false
+    t.string   "phone_number",            limit: 30
     t.string   "official_position"
     t.integer  "official_level",                     default: 0
     t.datetime "hidden_at"
-    t.string   "phone_number",            limit: 30
     t.string   "username"
   end
 
@@ -214,6 +224,7 @@ ActiveRecord::Schema.define(version: 20150824113326) do
   add_index "votes", ["voter_id", "voter_type", "vote_scope"], name: "index_votes_on_voter_id_and_voter_type_and_vote_scope", using: :btree
 
   add_foreign_key "administrators", "users"
+  add_foreign_key "identities", "users"
   add_foreign_key "inappropiate_flags", "users"
   add_foreign_key "moderators", "users"
   add_foreign_key "organizations", "users"
diff --git a/spec/factories.rb b/spec/factories.rb
index 038a0102e..4fa2a70e3 100644
--- a/spec/factories.rb
+++ b/spec/factories.rb
@@ -1,5 +1,4 @@
 FactoryGirl.define do
-
   factory :user do
     username         'Manuela'
     sequence(:email) { |n| "manuela#{n}@madrid.es" }
@@ -7,6 +6,12 @@ FactoryGirl.define do
     confirmed_at     { Time.now }
   end
 
+  factory :identity do
+    user nil
+    provider "Twitter"
+    uid "MyString"
+  end
+
   factory :debate do
     sequence(:title)     { |n| "Debate #{n} title" }
     description          'Debate description'
diff --git a/spec/features/users_spec.rb b/spec/features/users_spec.rb
index 42511f28c..1fa30bcbe 100644
--- a/spec/features/users_spec.rb
+++ b/spec/features/users_spec.rb
@@ -2,44 +2,159 @@ require 'rails_helper'
 
 feature 'Users' do
 
-  scenario 'Sign up' do
-    visit '/'
-    click_link 'Sign up'
+  context 'Regular authentication' do
+    scenario 'Sign up' do
+      visit '/'
+      click_link 'Sign up'
 
-    fill_in 'user_username',              with: 'Manuela Carmena'
-    fill_in 'user_email',                 with: 'manuela@madrid.es'
-    fill_in 'user_password',              with: 'judgementday'
-    fill_in 'user_password_confirmation', with: 'judgementday'
-    fill_in 'user_captcha',               with: correct_captcha_text
+      fill_in 'user_username',              with: 'Manuela Carmena'
+      fill_in 'user_email',                 with: 'manuela@madrid.es'
+      fill_in 'user_password',              with: 'judgementday'
+      fill_in 'user_password_confirmation', with: 'judgementday'
+      fill_in 'user_captcha',               with: correct_captcha_text
 
-    click_button 'Sign up'
+      click_button 'Sign up'
 
-    expect(page).to have_content "A message with a confirmation link has been sent to your email address. Please follow the link to activate your account."
+      expect(page).to have_content "A message with a confirmation link has been sent to your email address. Please follow the link to activate your account."
 
-    sent_token = /.*confirmation_token=(.*)".*/.match(ActionMailer::Base.deliveries.last.body.to_s)[1]
-    visit user_confirmation_path(confirmation_token: sent_token)
+      sent_token = /.*confirmation_token=(.*)".*/.match(ActionMailer::Base.deliveries.last.body.to_s)[1]
+      visit user_confirmation_path(confirmation_token: sent_token)
 
-    expect(page).to have_content "Your email address has been successfully confirmed"
+      expect(page).to have_content "Your email address has been successfully confirmed"
+    end
+
+    scenario 'Errors on sign up' do
+      visit '/'
+      click_link 'Sign up'
+      click_button 'Sign up'
+
+      expect(page).to have_content error_message
+    end
+
+    scenario 'Sign in' do
+      create(:user, email: 'manuela@madrid.es', password: 'judgementday')
+
+      visit '/'
+      click_link 'Log in'
+      fill_in 'user_email',    with: 'manuela@madrid.es'
+      fill_in 'user_password', with: 'judgementday'
+      click_button 'Log in'
+
+      expect(page).to have_content 'Signed in successfully.'
+    end
   end
 
-  scenario 'Errors on sign up' do
-    visit '/'
-    click_link 'Sign up'
-    click_button 'Sign up'
+  context 'OAuth authentication' do
+    context 'Twitter' do
+      background do
+        #request.env["devise.mapping"] = Devise.mappings[:user]
+      end
 
-    expect(page).to have_content error_message
-  end
+      scenario 'Sign up, when email was provided by OAuth provider' do
+        omniauth_twitter_hash = { 'provider' => 'twitter',
+                                  'uid' => '12345',
+                                  'info' => {
+                                    'name' => 'manuela',
+                                    'email' => 'manuelacarmena@example.com',
+                                    'nickname' => 'ManuelaRocks',
+                                    'verified' => '1'
+                                  },
+                                  'extra' => { 'raw_info' =>
+                                    { 'location' => 'Madrid',
+                                      'name' => 'Manuela de las Carmenas'
+                                    }
+                                  }
+                                }
 
-  scenario 'Sign in' do
-    create(:user, email: 'manuela@madrid.es', password: 'judgementday')
+        OmniAuth.config.add_mock(:twitter, omniauth_twitter_hash)
 
-    visit '/'
-    click_link 'Log in'
-    fill_in 'user_email',    with: 'manuela@madrid.es'
-    fill_in 'user_password', with: 'judgementday'
-    click_button 'Log in'
+        visit '/'
+        click_link 'Sign up'
 
-    expect(page).to have_content 'Signed in successfully.'
+        expect do
+          expect do
+            expect do
+              click_link 'Sign in with Twitter'
+            end.not_to change { ActionMailer::Base.deliveries.size }
+          end.to change { Identity.count }.by(1)
+        end.to change { User.count }.by(1)
+
+        expect(current_path).to eq(root_path)
+        expect_to_be_signed_in
+
+        user = User.last
+        expect(user.username).to eq('ManuelaRocks')
+        expect(user.email).to eq('manuelacarmena@example.com')
+        expect(user.confirmed?).to eq(true)
+      end
+
+      scenario 'Sign up, when neither email nor nickname were provided by OAuth provider' do
+        omniauth_twitter_hash = { 'provider' => 'twitter',
+                                  'uid' => '12345',
+                                  'info' => {
+                                    'name' => 'manuela'
+                                  },
+                                  'extra' => { 'raw_info' =>
+                                    { 'location' => 'Madrid',
+                                      'name' => 'Manuela de las Carmenas'
+                                    }
+                                  }
+                                }
+
+        OmniAuth.config.add_mock(:twitter, omniauth_twitter_hash)
+
+        visit '/'
+        click_link 'Sign up'
+
+        expect do
+          expect do
+            expect do
+              click_link 'Sign in with Twitter'
+            end.not_to change { ActionMailer::Base.deliveries.size }
+          end.to change { Identity.count }.by(1)
+        end.to change { User.count }.by(1)
+
+        expect(current_path).to eq(finish_signup_path)
+
+        user = User.last
+        expect(user.username).to eq('manuela-de-las-carmenas')
+        expect(user.email).to eq("omniauth@participacion-12345-twitter.com")
+
+        fill_in 'user_email', with: 'manueladelascarmenas@example.com'
+        click_button 'Sign up'
+
+        sent_token = /.*confirmation_token=(.*)".*/.match(ActionMailer::Base.deliveries.last.body.to_s)[1]
+        visit user_confirmation_path(confirmation_token: sent_token)
+
+        expect(page).to have_content "Your email address has been successfully confirmed"
+
+        expect(user.reload.email).to eq('manueladelascarmenas@example.com')
+      end
+
+      scenario 'Sign in, user was already signed up with OAuth' do
+        user = create(:user, email: 'manuela@madrid.es', password: 'judgementday')
+        identity = create(:identity, uid: '12345', provider: 'twitter', user: user)
+        omniauth_twitter_hash = { 'provider' => 'twitter',
+                                  'uid' => '12345',
+                                  'info' => {
+                                    'name' => 'manuela'
+                                  }
+                                }
+
+        OmniAuth.config.add_mock(:twitter, omniauth_twitter_hash)
+
+        visit '/'
+        click_link 'Log in'
+
+        expect do
+          expect do
+            click_link 'Sign in with Twitter'
+          end.not_to change { Identity.count }
+        end.not_to change { User.count }
+
+        expect_to_be_signed_in
+      end
+    end
   end
 
   scenario 'Sign out' do
@@ -73,5 +188,4 @@ feature 'Users' do
 
     expect(page).to have_content "Your password has been changed successfully. You are now signed in."
   end
-
 end
diff --git a/spec/models/identity_spec.rb b/spec/models/identity_spec.rb
new file mode 100644
index 000000000..82d5c4be3
--- /dev/null
+++ b/spec/models/identity_spec.rb
@@ -0,0 +1,9 @@
+require 'rails_helper'
+
+RSpec.describe Identity, type: :model do
+  let(:identity) { build(:identity) }
+
+  it "should be valid" do
+    expect(identity).to be_valid
+  end
+end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 5a4bbdf88..e0260285a 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -50,6 +50,26 @@ describe User do
     end
   end
 
+  describe 'OmniAuth' do
+    describe '#email_provided?' do
+      it "is false if the email matchs was temporarely assigned by the OmniAuth process" do
+        subject.email = 'omniauth@participacion-ABCD-twitter.com'
+        expect(subject.email_provided?).to eq(false)
+      end
+
+      it "is true if the email is not omniauth-like" do
+        subject.email = 'manuelacarmena@example.com'
+        expect(subject.email_provided?).to eq(true)
+      end
+
+      it "is true if the user's real email is pending to be confirmed" do
+        subject.email = 'omniauth@participacion-ABCD-twitter.com'
+        subject.unconfirmed_email = 'manuelacarmena@example.com'
+        expect(subject.email_provided?).to eq(true)
+      end
+    end
+  end
+
   describe "administrator?" do
     it "is false when the user is not an admin" do
       expect(subject.administrator?).to be false
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index d073cc173..c2f5db0fe 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -22,3 +22,5 @@ RSpec.configure do |config|
 end
 
 Capybara.javascript_driver = :poltergeist
+
+OmniAuth.config.test_mode = true
diff --git a/spec/support/common_actions.rb b/spec/support/common_actions.rb
index 21a98f56f..12d6affd3 100644
--- a/spec/support/common_actions.rb
+++ b/spec/support/common_actions.rb
@@ -77,4 +77,7 @@ module CommonActions
     /\d errors? prohibited this (.*) from being saved:/
   end
 
+  def expect_to_be_signed_in
+    expect(find('.top-bar')).to have_content 'My account'
+  end
 end