Configuring controllers

If the customization at the views level is not enough, you can customize each controller by following these steps:

Create your custom controllers using the generator which requires a scope:
```
$ rails generate devise:controllers [scope]
```
If you specify users as the scope, controllers will be created in app/controllers/users/. And the sessions controller will look like this:
```
class Users::SessionsController < Devise::SessionsController
  # GET /resource/sign_in
  # def new
  #   super
  # end
  ...
end
```
(Use the -c flag to specify a controller, for example: rails generate devise:controllers users -c=sessions)

Tell the router to use this controller:

devise_for :users, controllers: { sessions: 'users/sessions' }

Copy the views from devise/sessions to users/sessions. Since the controller was changed, it won't use the default views located in devise/sessions.

Finally, change or extend the desired controller actions.

You can completely override a controller action:

class Users::SessionsController < Devise::SessionsController
  def create
    # custom sign-in code
  end
end

Or you can simply add new behaviour to it:

class Users::SessionsController < Devise::SessionsController
  def create
    super do |resource|
      BackgroundWorker.trigger(resource)
    end
  end
end

This is useful for triggering background jobs or logging events during certain actions.

Remember that Devise uses flash messages to let users know if sign in was successful or unsuccessful. Devise expects your application to call flash[:notice] and flash[:alert] as appropriate. Do not print the entire flash hash, print only specific keys. In some circumstances, Devise adds a :timedout key to the flash hash, which is not meant for display. Remove this key from the hash if you intend to print the entire hash.