app/controllers/api/v1/application_controller.rb
module Api
  module V1
    class ApplicationController < ApplicationController
      include DeviseTokenAuth::Concerns::SetUserByToken
      protect_from_forgery with: :null_session
      before_action :authenticate_api_v1_user!
      respond_to :json
    end
  end
end

app/controllers/api/v1/application_controller.rb
module Users
  class ApplicationController < ApplicationController
    before_action :authenticate_user!
  end
end

app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
end

config/routes.rb
Rails.application.routes.draw do
  devise_for :users, controllers: { sessions: 'user_sessions', registrations: 'user_registrations' }
  namespace :api do
    scope :v1 do
      mount_devise_token_auth_for 'User', at: 'auth'
    end
  end
  root "cluster#index"
  get "get_config"               => "cluster#get_config"
  resources :users
end

app/controllers/cluster_controller.rb
class ClusterController < ApplicationController
  def index
    respond_to do |format|
      format.html  # index.html.erb
    end
  end
  def get_config
    render json: [config]
  end
end