application_controller.rb

class ApplicationController < ActionController::Base
  include SessionsHelper
  protect_from_forgery with: :exception
 
end

sessions_helper.rb

module SessionsHelper
  def sign_in(user)
    remember_token = User.new_remember_token
    cookies.permanent[:remember_token] = remember_token
    user.update_attribute(:remember_token, User.encrypt(remember_token))
    self.current_user = user
  end
  
  def signed_in?
    !current_user.nil?
  end
  
  def sign_out
    self.current_user = nil
    cookies.delete(:remember_token)
  end
 
  def current_user=(user)
    @current_user = user
  end

  def current_user
    remember_token = User.encrypt(cookies[:remember_token])
    @current_user ||= User.find_by(remember_token: remember_token)
  end
  
  
end

users_controller.rb

class UsersController < ApplicationController
  
  def new
      @user = User.new
  end
  
  def create
    @user = User.new(user_params)
      if @user.save
        sign_in @user
        flash[:success]= "Registration success!"
        redirect_to @user
      else
        render 'new'
     end 
  end
  
  def show
    #if signed_in?
      @user = User.find(params[:id])
    #end
  end
  private
  def user_params
    params.require(:user).permit(:name, :email, :password, :password_confirmation)
  end
  
end