calefaction/app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  before_action :load_user

  private
  def load_user
    @user = User.find_by(id: session[:user_id]) if session[:user_id]
  end
end