Working with Facebook using Devise, Omniauth, Koala and Rails 5

First of all, we need to setup our Facebook app. There’s not much to add on this, simply create a new Facebook app if needed. When your app is created, make sure to add the proper app domain. In this case, the app domain will be localhost to allow us to test it locally, but it should be changed to work properly on your staging or production environment. Also, make sure to add a platform according to what kind of application you’re working on. Here I selected a website and the site URL should match the app domain.