Ruby on Rails Remember Me Log In Not Working

I am following the following tutorial:

http://ift.tt/1drzuZt

And have just tried to add the 'remember me' functionality, so only up to around 4 minutes of the tutorial.

Everything seems fine but once I try to log in it just goes back to the home page and no one is logged in.

User.rb:

before_create { generate_token(:auth_token) 

def generate_token(column)
  begin
    self[column] = SecureRandom.urlsafe_base64
  end while User.exists?(column => self[column])
end

sessions_controller:

def create
    user = User.find_by email: params[:email]
    if user and user.authenticate params[:password]
        # 'logging in' is performed by saving a user's id in the session variable
        #session[:user_id] = user.id
        #cookies.permanent[:auth_token] = user.auth_token
        if params[:remember_me]
          cookies.permanent[:auth_token] = user.auth_token
        else
          cookies[:auth_token] = user.auth_token
        end
        # redirect to last page or root_path (products/index.html.erb')
        redirect_to root_path
    else
        flash.now.notice = "Invalid user/password"
        render :new
    end
end


def destroy     
    # the act of logging out is performed by simply setting the key (:user_id)      
    # in the session hash to a value of nil (nothing)                   
    #session[:user_id] = nil
    cookies.delete(:auth_token)     
    # redirect to root_path (products/index.html.erb') 
    redirect_to root_path 
end

application_controller:

def authenticate_user
    # if session[:user_id]
        # @current_user = User.find session[:user_id]
    # else
        # @current_user = nil
    # end
    if cookies[:auth_token]
        @current_user ||= User.find_by_auth_token!(cookies[:auth_token]) 
    else
        @current_user = nil
    end
end

Can someone please tell me what the problem is.