Introduction

OAuth2 is a protocol that allows secure authorization in a simple and standardized way. By implementing OAuth2 providers, you enable your Rails application to allow users to authenticate via third-party services such as Google, Facebook, GitHub, or custom OAuth2 services.

In this post, we will walk through the process of implementing an OAuth2 provider in a Rails application, step by step, to help you securely integrate with external authentication systems.

1. What is OAuth2?

OAuth2 (Open Authorization 2) is a protocol for granting access to applications without sharing passwords. OAuth2 enables users to authenticate using third-party services while keeping their credentials private. The flow involves:

  1. Authorization Request – A user is redirected to the OAuth2 provider’s authorization endpoint.
  2. Token Exchange – After authorization, the provider returns an access token to the application.
  3. Accessing Protected Resources – The access token allows the application to access protected resources on behalf of the user.

OAuth2 is a widely adopted protocol for implementing secure, scalable authentication mechanisms in web applications.

2. Setting Up OAuth2 Provider in Rails

In Rails, we can implement an OAuth2 provider using gems such as Doorkeeper or OmniAuth. In this tutorial, we will use Doorkeeper to create an OAuth2 provider.

Step 1: Install Doorkeeper Gem

Add Doorkeeper to your Gemfile:

gem 'doorkeeper'

Run the bundle command to install it:

bundle install
Step 2: Generate Doorkeeper Configuration

Generate the Doorkeeper configuration files:

rails generate doorkeeper:install  
rails db:migrate

This will create the necessary database tables for storing OAuth2 tokens and client credentials.

Step 3: Configure OAuth2 Providers

In your config/initializers/doorkeeper.rb, you can define your OAuth2 provider settings. For example:

Doorkeeper.configure do
# Enable password grant flow (typically used by web apps)
grant_flows %w[authorization_code client_credentials password]

# Define the path for authorization request
resource_owner_from_credentials do |routes|  
User.find_by_email(routes[:username])  
end

# Customize token expiration time
access_token_expires_in 2.hours  
end
Step 4: Set Up OAuth Routes

Doorkeeper automatically sets up the routes required for OAuth2 authentication. However, you might want to create custom controllers to handle the token exchange process. You can access the /oauth/authorize and /oauth/token routes to handle OAuth2 flows.

3. Implementing the Authorization Flow

Once the OAuth2 provider is set up, you need to implement the Authorization Flow. When a user requests authentication, they will be redirected to the provider’s authorization URL, where they will grant the necessary permissions.

Step 1: Implement the Authorization Endpoint

Create an endpoint in your Rails application to redirect the user to the OAuth provider’s authorization page:

class AuthorizationsController < ApplicationController  
def new  
redirect_to oauth_provider_authorization_url  
end  
end
Step 2: Handle the Redirect and Token Exchange

Once the user is authorized, they are redirected back to your application with an authorization code. You can exchange this code for an access token:

class OauthCallbacksController < ApplicationController  
def create  
response = doorkeeper_token.exchange_token(params[:code])  
# Store the access token  
session[:access_token] = response['access_token']  
redirect_to dashboard_path  
end  
end

4. Securing API Endpoints with OAuth2 Tokens

Once the user is authenticated, you can secure your API endpoints by verifying the access token. You can use Doorkeeper’s built-in before_action filters to protect routes:

class ApiController < ApplicationController  
before_action :doorkeeper_authorize!

def show  
render json: { message: "Secure API content" }  
end  
end

This ensures that only authenticated requests with valid tokens can access protected resources.

5. Testing OAuth2 Authentication

When testing OAuth2 integration, it’s important to simulate the authorization flow. Use Rails’ built-in test helpers along with VCR or WebMock to mock OAuth2 responses.

You can test the token exchange and authentication flow as follows:

require 'test_helper'

class OauthCallbacksControllerTest < ActionDispatch::IntegrationTest  
test "should create access token" do  
post oauth_callbacks_url, params: { code: 'sample_authorization_code' }  
assert_response :redirect  
assert_not_nil session[:access_token]  
end  
end

6. Best Practices for OAuth2 Implementations in Rails

  • Use Secure Tokens – Always store tokens securely, and consider encrypting them in the database.
  • Refresh Tokens – Use refresh tokens to allow users to stay authenticated without repeatedly re-entering their credentials.
  • Limit Scopes – Only request the minimum permissions necessary for your application to function.
  • Handle Token Expiry – Ensure that expired tokens are gracefully handled, and prompt users to reauthorize when necessary.

Conclusion

Implementing OAuth2 providers in Rails enables your application to securely integrate with third-party services for authentication. By following best practices, you can provide a seamless and secure experience for your users.

Key Takeaways:

  • Use Doorkeeper to implement OAuth2 provider functionality.
  • Protect API endpoints with OAuth2 tokens.
  • Test and simulate the OAuth2 flow during development.

OAuth2 implementation in Rails ensures your application is scalable, secure, and easy to maintain, allowing users to authenticate with popular third-party services effortlessly.