authentication.rb

# app/controllers/concerns/authentication.rb
# (Authorisation is different than Authentication and so it is handled in a different concern)

module Authentication
  extend ActiveSupport::Concern

  included do
    before_action :authenticate
    helper_method :logged_in?
  end

  private

  def logged_in?
    Current.person.present?
  end

  def authenticate
    if authenticated_user = Person.find_by(id: session[:person_id])
      Current.person = authenticated_user
    end
  end

  def sign_in(person)
    session[:person_id] = person.id
  end
end