Ruby On Rails API: Authentication

View on Github

Ruby On Rails API: Authentication

Gravatar for andres.aguiar@auth0.com
By Andres Aguiar
Auth0

This tutorial demonstrates how to add authorization to a Ruby on Rails API. We recommend you to Log in to follow this quickstart with examples configured for your account.

Or

I want to explore a sample app

2 minutes

Get a sample configured with your account settings or check it on Github.

View on Github
System requirements: Ruby 2.1.8 | Rails 4.2.5

New to Auth? Learn How Auth0 works and read about API authorization.

Configure Auth0 APIs

Create an API

In the APIs section of the Auth0 dashboard, click Create API. Provide a name and an identifier for your API, for example https://quickstarts/api. You will use the identifier as an audience later, when you are configuring the Access Token verification. For Signing Algorithm, select RS256.

Create API

By default, your API uses RS256 as the algorithm for signing tokens. Since RS256 uses a private/public keypair, it verifies the tokens against the public key for your Auth0 account. The public key is in the JSON Web Key Set (JWKS) format, and can be accessed here.

We recommend using the default RS256 signing algorithm for your API. If you need to use the HS256 algorithm, see the HS256 integration sample.

Define scopes

Scopes let you define which resources can be accessed by the user with a given Access Token. For example, you might choose to grant read access to the messages resource if users have the manager access level, and a write access to that resource if they have the administrator access level.

You can add the required scopes in the Scopes tab of the Auth0 Dashboard's APIs section.

Configure Scopes

This example uses the read:messages scope.

This example demonstrates:

  • How to check for a JSON Web Token (JWT) in the Authorization header of an incoming HTTP request.

  • How to check if the token is valid, using the JSON Web Key Set (JWKS) for your Auth0 account. To learn more about validating Access Tokens, read the Verify Access Tokens tutorial.

Validate Access Tokens

Install dependencies

This tutorial performs Access Token validation using the jwt Gem within a custom JsonWebToken class. A Concern called Secured is used to mark endpoints which require authentication through an incoming Access Token.

Install the jwt Gem.

gem `jwt`
bundle install

Create a JsonWebToken class

Create a class called JsonWebToken which decodes and verifies the incoming Access Token taken from the Authorization header of the request. The public key for your Auth0 tenant can be fetched to verify the token.

# lib/json_web_token.rb

# frozen_string_literal: true
require 'net/http'
require 'uri'

class JsonWebToken
  def self.verify(token)
    JWT.decode(token, nil,
               true, # Verify the signature of this token
               algorithm: 'RS256',
               iss: 'https://YOUR_AUTH0_DOMAIN/',
               verify_iss: true,
               aud: Rails.application.secrets.auth0_api_audience,
               verify_aud: true) do |header|
      jwks_hash[header['kid']]
    end
  end

  def self.jwks_hash
    jwks_raw = Net::HTTP.get URI("https://YOUR_AUTH0_DOMAIN/.well-known/jwks.json")
    jwks_keys = Array(JSON.parse(jwks_raw)['keys'])
    Hash[
      jwks_keys
      .map do |k|
        [
          k['kid'],
          OpenSSL::X509::Certificate.new(
            Base64.decode64(k['x5c'].first)
          ).public_key
        ]
      end
    ]
  end
end

Define a Secured concern

Create a Concern called Secured which looks for the Access Token in the Authorization header of an incoming request. If the token is present, it should be passed to JsonWebToken.verify.

# app/controllers/concerns/secured.rb

# frozen_string_literal: true
module Secured
  extend ActiveSupport::Concern

  included do
    before_action :authenticate_request!
  end

  private

  def authenticate_request!
    auth_token
  rescue JWT::VerificationError, JWT::DecodeError
    render json: { errors: ['Not Authenticated'] }, status: :unauthorized
  end

  def http_token
    if request.headers['Authorization'].present?
      request.headers['Authorization'].split(' ').last
    end
  end

  def auth_token
    JsonWebToken.verify(http_token)
  end
end

Validate scopes

The JsonWebToken.verify method above verifies that the Access Token included in the request is valid; however, it doesn't yet include any mechanism for checking that the token has the sufficient scope to access the requested resources.

To look for a particular scope in an Access Token, provide an array of required scopes and check if they are present in the payload of the token.

In this example we define an SCOPES array for all protected routes, specifying the required scopes for each one. For the /private-scoped route, the scopes defined will be intersected with the scopes coming in the payload, to determine if it contains one or more items from the other array.

# app/controllers/concerns/secured.rb

  SCOPES = {
    '/private' => nil,
    '/private-scoped'    => ['read:messages']
  }

  private

  def authenticate_request!
    @auth_payload, @auth_header = auth_token

    render json: { errors: ['Insufficient scope'] }, status: :unauthorized unless scope_included
  rescue JWT::VerificationError, JWT::DecodeError
    render json: { errors: ['Not Authenticated'] }, status: :unauthorized
  end

  def scope_included
    if SCOPES[request.env['PATH_INFO']] == nil
      true
    else
      # The intersection of the scopes included in the given JWT and the ones in the SCOPES hash needed to access
      # the PATH_INFO, should contain at least one element
      (String(@auth_payload['scope']).split(' ') & (SCOPES[request.env['PATH_INFO']])).any?
    end
  end

Protect API Endpoints

The routes shown below are available for the following requests:

  • GET /api/public: available for non-authenticated requests
  • GET /api/private: available for authenticated requests containing an Access Token with no additional scopes
  • GET /api/private-scoped: available for authenticated requests containing an Access Token with the read:messages scope granted

The /public endpoint does not require to use the Secured concern.

# app/controllers/public_controller.rb

# frozen_string_literal: true
class PublicController < ActionController::API
  # This route doesn't need authentication
  def public
    render json: { message: 'Hello from a public endpoint! You don't need to be authenticated to see this.' }
  end
end

The protected endpoints need to include the Secured concern. The scopes required for each one are defined in the code of the Secured concern.

# app/controllers/private_controller.rb

# frozen_string_literal: true
class PrivateController < ActionController::API
  include Secured

  def private
    render json: 'Hello from a private endpoint! You need to be authenticated to see this.'
  end

  def private_scoped
    render json: { message: 'Hello from a private endpoint! You need to be authenticated and have a scope of read:messages to see this.' }
  end
end

Use Auth0 for FREE