Twitter authentication

application_controller.rb

class ApplicationController < ActionController::Base
  protect_from_forgery

  helper_method :current_user, :signed_in?, :signed_out?
  hide_action   :current_user, :current_user=,
                :signed_in?,   :signed_out?,
                :sign_in,      :sign_out,
                :authorize,    :deny_access

  def current_user
    @_current_user ||= user_from_cookie
  end

  def current_user=(user)
    @_current_user = user
  end

  def signed_in?
    ! current_user.nil?
  end

  def signed_out?
    current_user.nil?
  end

  def sign_in(user)
    if user
      cookies[:remember_token] = {
        :value   => user.remember_token,
        :expires => 1.year.from_now
      }
      self.current_user = user
    end
  end

  def sign_out
    current_user.reset_remember_token! if current_user
    cookies.delete(:remember_token)
    self.current_user = nil
  end

  def authorize
    deny_access unless signed_in?
  end

  def deny_access
    store_location
    if signed_in?
      redirect_to root_path
    else
      redirect_to '/auth/twitter'
    end
  end

  protected

  def user_from_cookie
    if token = cookies[:remember_token]
      User.find_by_remember_token(token)
    end
  end

  def store_location
    if request.get?
      session[:return_to] = request.fullpath
    end
  end

  def redirect_back_or(default)
    redirect_to(return_to || default)
    clear_return_to
  end

  def return_to
    session[:return_to] || params[:return_to]
  end

  def clear_return_to
    session[:return_to] = nil
  end

  def redirect_to_root
    redirect_to('/')
  end
end

Gemfile

gem "omniauth-twitter"

intializer.rb

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :developer unless Rails.env.production?
  provider :twitter, ENV['TWITTER_KEY'], ENV['TWITTER_SECRET']
end

migration.rb

class CreateDieselClearanceUsers < ActiveRecord::Migration
  def self.up
    create_table(:users) do |t|
      t.string   :provider,    default: "",   null: false
      t.string   :uid,         default: "",   null: false
      t.string   :name,        default: "",   null: false
      t.string   :twitter,     default: "",   null: false
      t.string   :location,    default: "",   null: false
      t.string   :remember_token, limit: 128
      t.timestamps
    end

    add_index :users, :remember_token
    add_index :users, [:provider, :uid]
    add_index :users, :twitter
  end

  def self.down
    drop_table :users
  end
end

sessions_controller.rb

class SessionsController < ApplicationController
  def create
    sign_in User.find_or_create_by_auth(request.env["omniauth.auth"])
    redirect_to root_path
  end

  def destroy
    sign_out
    redirect_to root_path
  end
end

user.rb

class User < ActiveRecord::Base
  before_create :generate_remember_token

  def self.find_or_create_by_auth(auth)
    find_by_provider_and_uid(auth["provider"], auth["uid"]) ||

    create do |user|
      user.provider  = auth["provider"]
      user.uid       = auth["uid"]
      user.name      = auth["info"]["name"]
      user.twitter   = auth["info"]["nickname"]
      user.location  = auth["info"]["location"]
    end
  end

  protected

  def generate_remember_token
    self.remember_token = SecureRandom.hex(20).encode('UTF-8')
  end
end