Ruby API: Authorization

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Ruby API: Authorization

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

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System requirements: Ruby 2.3.0

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.

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. An authenticate! method 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 from the Authorization header of the request. The public key for your Auth0 tenant can be fetched to verify the token.

# lib/jwt/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,
               # auth0_api_audience is the identifier for the API set up in the Auth0 dashboard
               aud: 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

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 the SCOPES array for the given key /api/private-scoped is intersected with the scopes contained in the payload of the Access Token to determine if it contains one or more items from the array.

# lib/server_rs256.rb

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

def authenticate!
  # Extract <token> from the 'Bearer <token>' value of the Authorization header
  supplied_token = String(request.env['HTTP_AUTHORIZATION']).slice(7..-1)

  @auth_payload, @auth_header = JsonWebToken.verify(supplied_token)

  halt 403, json(error: 'Forbidden', message: 'Insufficient scope') unless scope_included

rescue JWT::DecodeError => e
  halt 401, json(error: e.class, message: e.message)
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

Define an authenticate! method

Create an authenticate! method to run before each endpoint 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.

# lib/server_rs256.rb

def authenticate!
  # Extract <token> from the 'Bearer <token>' value of the Authorization header
  supplied_token = String(request.env['HTTP_AUTHORIZATION']).slice(7..-1)

  @auth_payload, @auth_header = JsonWebToken.verify(supplied_token)

rescue JWT::DecodeError => e
  halt 401, json(error: e.class, message: e.message)
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 authenticate! method.

get '/api/public' do
  json( message: 'Hello from a public endpoint! You don't need to be authenticated to see this.' )
end

The protected endpoints need to include the authenticate! method. The scopes required for each one are defined in the code of the authenticate! method.

get '/api/private' do
  authenticate!
  json( message: 'Hello from a private endpoint! You need to be authenticated to see this.' )
end

get '/api/private-scoped' do
  authenticate!
  json( message: 'Hello from a private endpoint! You need to be authenticated and have a scope of read:messages to see this.' )
end
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