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Some setup you must do manually if you haven't yet:

  1. Ensure you have overridden or uncommented the routes for generated omniauth callback controllers in your routes.rb.
     For example:

     Rails.application.routes.draw do
       devise_for :users, controllers: {
         omniauth_callbacks: "users/omniauth_callbacks"
       }
     end

  2. Update the devise google omniauth APP_ID and APP_SECRET in "config/initializers/devise.rb"
     after registering the Rails application on: https://code.google.com/apis/console/
     For example:

     config.omniauth :google_auth, "APP_ID", "APP_SECRET"

  3. Your omniauth callback URL will be: `<host>/users/auth/google_oauth2/callback`. Please update
     callback URL in Google after registering your omniauth application.

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