Ruby API Authorization

Sample Project

Download a sample project specific to this tutorial configured with your Auth0 API Keys.

System Requirements
  • Ruby 2.3.0
Show requirements

To restrict access to the resources served by your API, a check needs to be made to determine whether the incoming request contains valid authorization information. There are various methods for including authorization information in a request, but for integration with Auth0, your API needs to check for a valid JSON Web Token (JWT). When users log into your application, they will receive an id_token and an access_token which are both JWTs. The specific JWT that needs to be sent to your API is the access_token.

This sample demonstrates how to check for a JWT in the Authorization header of an incoming HTTP request and verify that it is valid. The validity check is done 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. If the token is valid, the resources which are served by the endpoint can be released, otherwise a 401 Authorization error will be returned.

Install the Dependencies

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 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

Define an authentincate! 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

before do
  authenticate!
end

get '/restricted_resource' do
  json( message: 'Access Granted', allowed_scopes: String(@auth_payload['scope']).split(' ') )
end

Configure 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.

Scopes provide a way for you to define which resources should be accessible by the user holding a given access_token. For example, you might choose to permit read access to a messages resource if a user has a manager access level, or write access to that resource if they are an administrator.

To configure scopes in your Auth0 dashboard, navigate to your API and choose the Scopes tab. In this area you can apply any scopes you wish, including one called read:messages, which will be used in this example.

Protect Individual Endpoints

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 /restricted_resource 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/jwt/json_web_token.rb

SCOPES = {
  '/restricted_resource' => ['read:messages'],
  '/another_resource'    => ['some:scope', 'some:other_scope']
}

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
  # 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

With this configuration in place, only access_tokens which have a scope of read:messages will be allowed to access this endpoint.

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