Best Practices for Authentication and Authorization in Rails

1. Introduction

The goal of this tutorial is to give you a solid understanding of the best practices for implementing authentication and authorization in Rails. You'll learn how to securely manage user access to your application, and how to restrict access to certain parts of your app based on user roles.

You will learn:
- The difference between authentication and authorization
- How to implement authentication using sessions and cookies
- How to implement authorization using roles and permissions

Prerequisites:
- Basic knowledge of Ruby on Rails
- Familiarity with HTML and CSS
- Understanding of MVC architecture

2. Step-by-Step Guide

Authentication: Authentication is the process of verifying the identity of a user, device, or system. It often involves a username and password, but can involve any method of demonstrating identity, such as a smart card, retina scan, voice recognition, or fingerprints.

Authorization: Authorization is the process of giving someone permission to do or have something. In multi-user systems, a system administrator defines for the system which users are allowed access to the system and what privileges of use.

Authentication with Devise

Devise is a flexible authentication solution for Rails. It handles all of the complexity of implementing user authentication, including registration, login, and password reset.

Install Devise

gem 'devise'

After adding the gem to your Gemfile, run bundle install to install it. Then, run rails generate devise:install to create the necessary configuration files.

Create a User model

rails generate devise User

This will generate a User model with some Devise modules. Run rails db:migrate to create the users table.

Authorization with Pundit

Pundit provides a set of helpers which guide you in leveraging regular Ruby classes and object-oriented design patterns to build a simple, robust and scalable authorization system.

Install Pundit

gem 'pundit'

After adding the gem, run bundle install and then rails generate pundit:install to generate the application policy.

Authorization: Roles and Permissions

A common approach to authorization is to assign roles to users, and permissions to roles. A user gains the permissions of the roles they have.

class User < ApplicationRecord
  enum role: { guest: 0, user: 1, admin: 2 }
end

This will add convenience methods like user.admin? which will return true if the user's role is 'admin'.

3. Code Examples

Example 1: User Registration with Devise

# app/controllers/users/registrations_controller.rb
class Users::RegistrationsController < Devise::RegistrationsController
  # POST /resource
  def create
    build_resource(sign_up_params)

    resource.save
    yield resource if block_given?
    if resource.persisted?
      if resource.active_for_authentication?
        set_flash_message! :notice, :signed_up
        sign_up(resource_name, resource)
        respond_with resource, location: after_sign_up_path_for(resource)
      else
        set_flash_message! :notice, :"signed_up_but_#{resource.inactive_message}"
        expire_data_after_sign_in!
        respond_with resource, location: after_inactive_sign_up_path_for(resource)
      end
    else
      clean_up_passwords resource
      set_minimum_password_length
      respond_with resource
    end
  end
end

Example 2: User Authorization with Pundit

# app/policies/article_policy.rb
class ArticlePolicy < ApplicationPolicy
  def update?
    user.admin? or not record.published?
  end
end

This policy allows admins to update any articles, and allows other users to update only unpublished articles.

4. Summary

You've learned about authentication and authorization, and how to implement them in Rails using Devise and Pundit. You also learned about using roles and permissions for authorization.

Next steps:
- Try implementing different types of user roles
- Experiment with different permissions for each role
- Learn more about Devise and Pundit

Additional resources:
- Devise Documentation
- Pundit Documentation

5. Practice Exercises

Exercise 1: Implement a user registration form with Devise.

Exercise 2: Create a policy with Pundit that allows only admins to delete users.

Exercise 3: Extend the User model with more roles, and create a policy for each role.

Happy coding!