Rails Login with google+

Step 1:
    In gemfile added gem:-

    gem "omniauth-google-oauth2"

Step 2:
       Go to 'https://console.developers.google.com'
Step 3:
    config/initializers/devise.rb:-

    config.omniauth :google_oauth2, ['client_id', 'secret_key']

Step 4:
create omniauth_callbacks_controller

devise/omniauth_callbacks_controller.rb

class Devise::OmniauthCallbacksController < ApplicationController

def google_oauth2
begin
   @user = User.find_for_google_oauth2(request.env['omniauth.auth'], session[:provider])
   session[:user_id] = @user.id
   sign_in @user
   session[:provider] = nil
   flash[:success] = "Welcome, #{@user.name}!"
 rescue
   flash[:warning] = "There was an error while trying to authenticate you..."
 end
 redirect_to after_sign_in_path_for(@user)

end

      def failure
        redirect_to root_path
     end

end

Step 5:
   config/routes:

    devise_for :users, :controllers => {:omniauth_callbacks => "devise/omniauth_callbacks" }
      get 'auth/:provider/callback', to: 'sessions#create'
      get 'logout', to: 'sessions#destroy'
      get 'failure' => 'devise/omniauth_callbacks#google_oauth2'

      get 'google_oauth2' => 'devise/omniauth_callbacks#google_oauth2'

Step 6:
   app/model/user.rb

     def self.find_for_google_oauth2(access_token, signed_in_resource=nil)
       data = access_token.info
       domain_info = data.email.split("@").last
       if domain_info == "ascratech.com" or domain_info == "ascratech.in"
         user = User.where(:email => data["email"], :provider => "google").first
         unless user
        devise_user = User.find_by_email(data["email"])
        unless devise_user
           user = User.new(:name => data["name"],
                           :provider => "google",
                           :email => data["email"],
                           :password => Devise.friendly_token[0,20]
                          )

           user.skip_confirmation!
            user.save
        else
          devise_user.provider = "google"
          devise_user.name = data["name"]
          devise_user.save
          user = devise_user
        end
      end
      return user
    end
  end