How to do Stateless User Authentication of My App - ruby-on-rails

Question

Update from comments: I want to do Stateless of Restful in HTTP connection. My goal is making a system that when users log into my app, my app's server assigns an id to them. Because if my app cannot do so, other users can access a user pages (if they write something in the URL randomly). And my server's model have users' ids in that time. When users log out my app, these ids are deleted from model. Maybe I can call these system 'Session'.
I am performing user authentication in my app. I want to realize Stateless in there that it pass id to users when they log in my app. However, I'm a beginner, so I don't know how to do it. I think I should write these codes in the main controller, but am not sure. How can I do this process?
home_controller
class HomeController < ApplicationController
before_filter :find_user, only: [:index]
def index
#id = params[:id]
#email = [:email]
if #id == #user.id && #email == #user.email
render :text => "sucsess"
else
render :text => "fail"
end
end
def create
userData = UserData.new(create_params)
user = User.find(params[:id]).to_json
# エラー処理
unless userData.save
#error_message = [memo.errors.full_messages].compact
end
end
private
　　 def find_user
#user = User.find(params[:id]) # You should specify this code what are your comparing to.
end
end
routes.rb
Rails.application.routes.draw do
devise_for :users
root to: "home#index"
get 'home/index'
namespace :home, default: {format: :json} do
resources :index, only: :create
end
end
user.rb
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable, :omniauthable
end

Answer 1

When a user logs in via Devise, they are given a unique token that is stored in the browser's session. When the next page is rendered, the browser will pass it's session cookie to the rails app, and Devise will gather the user token from the session cookie and populate the current_user variable with the user object that matches that token.
So if you follow the instructions for setting up Devise in its README, then once a user has logged in, you can access that logged in user's User object via current_user