どうでしょう（Rails4コントローラ用Concern）

authenticatable.rb

module Authenticatable
  extend ActiveSupport::Concern

  included do
    helper_method :current_user, :signed_in?, :me?, :own?
  end

  module Exceptions
    class Exception < SecurityError; end # SecurityError でいいのか謎
    class SignInRequired < Exception; end
    class SignInFailed < Exception; end
    class AccessDenied < Exception; end
  end

  module ClassMethods
    def require_sign_in (*args, &block)
      before_action :sign_in_required!, *args, &block
    end
  end

  def require_sign_in!
    raise Exceptions::SignInRequired
  end

  def sign_in_required!
    require_sign_in! unless signed_in?
  end
  
  def signed_in?
    not current_user.nil?
  end

  def sign_in_force (user)
    @current_user     = nil
    session[:user_id] = user.id
  end

  def sign_in (user, password)
    if signed_in = !! (user && user.authenticate(password))
      sign_in_force user
    end

    signed_in
  end

  def sign_in! (user, password)
    raise Exceptions::SignInFailed unless sign_in(user, password)
  end

  def sign_out!
    @current_user     = nil
    session[:user_id] = nil

    reset_session
  end

  def current_user
    @current_user ||= User.find_by(id: session[:user_id]) if session[:user_id]
  end

  def me? (user)
    signed_in? and current_user.id == user.id
  end

  def own? (record, association_key = :user_id)
    signed_in? and current_user.id == record.send(association_key)
  end

  def forbid_unless_me! (user)
    forbidden! unless me? user
  end
  
  def forbid_unless_own! (record, association_key = :user_id)
    forbidden! unless own? record, association_key
  end

  def forbidden! (message = nil)
    raise Exceptions::AccessDenied.new(message)
  end

end

examples_controller.rb

class ExamplesController < ApplicationController
  include Authenticatable

  require_sign_in except: [:action_sign_in_not_required]
  
  rescue_from Authenticatable::Exceptions::Exception do |exception|
    render status: 403, text: exception.message
  end
  
  def action_sign_in_not_required
  
  end
  
  def index
    @nyans = Nyan.where(user_id: current_user.id)
  end
  
  def edit
    @nyan = Nyan.find(params[:id])
    forbid_unless_own! @nyan
  end
  
  def require_sign_in!
    redirect_to signin_url
  end

end