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Node.js API Implementation (SPAs + API)

This document is part of the SPA + API Architecture Scenario and it explains how to implement the API in Node.js. Please refer to the scenario for information on the implemented solution. The full source code for the Node.js API implementation can be found in this GitHub repository.

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Step 1. Define the API endpoints

We will use the Express web application framework to build our Node.js API.

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Create a package.json File

Create a folder for your API, navigate into it and run npm init. This will setup your package.json file. You can leave the default settings or change them as you see fit. Our sample’s package.json looks like the following: 
{
  "name": "timesheets-api",
  "version": "1.0.0",
  "description": "API used to add timesheet entries for employees and contractors",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/auth0-samples/auth0-pnp-timesheets.git"
  },
  "author": "Auth0",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/auth0-samples/auth0-pnp-timesheets/issues"
  },
  "homepage": "https://github.com/auth0-samples/auth0-pnp-timesheets#readme"
}

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Install the Dependencies

Next, we need to set our dependencies. We will use the following modules:
  • express: This module adds the Express web application framework.
  • cors: This module adds support for enabling CORS which is required since the API will be called from a Single-Page Application running on a different domain inside a web browser.
  • jwks-rsa: This library retrieves RSA signing keys from a JWKS (JSON Web Key Set) endpoint. Using expressJwtSecret we can generate a secret provider that will provide the right signing key to express-jwt based on the kid in the header. For more information refer to the node-jwks-rsa GitHub repository.
  • express-jwt: This module lets you authenticate HTTP requests using JWT tokens in your Node.js applications. It provides several functions that make working with JWTs easier. For more information refer to the express-jwt GitHub repository.
  • body-parser: This is a Node.js body parsing middleware. It extracts the entire body portion of an incoming request stream and exposes it on req.body as something easier to interface with.For more information and several alternatives refer to the body-parser GitHub repository.
To install these dependencies run the following: 
npm install express cors express-jwt jwks-rsa body-parser express-jwt-authz --save

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Implement the Endpoints

Navigate to your API directory and create a server.js file. Your code needs to:
  • Get the dependencies.
  • Implement the endpoint(s).
  • Launch the API server.
This is our sample implementation: 
const express = require('express');
const app = express();
const { expressjwt: jwt } = require('express-jwt');
const jwksRsa = require('jwks-rsa');
const cors = require('cors');
const bodyParser = require('body-parser');

// Enable CORS
app.use(cors());

// Enable the use of request body parsing middleware
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));

// Create timesheets API endpoint
app.post('/timesheets', function(req, res){
  res.status(201).send({message: "This is the POST /timesheets endpoint"});
})

// Launch the API Server at localhost:8080
app.listen(8080);
Launch your API server using node server and make an HTTP POST request to localhost:8080/timesheets. You should see a JSON response with the message This is the POST /timesheets endpoint. So now we have our endpoint but anyone can call it. Continue to the next paragraph to see how we can fix this.

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Step 2. Secure the API endpoints

In order to validate our token we will use the jwt function, provided by the express-jwt middleware, and the jwks-rsa to retrieve our secret. The libraries do the following:
  1. express-jwt will decode the token and pass the request, the header and the payload to jwksRsa.expressJwtSecret.
  2. jwks-rsa will then download all signing keys from the JWKS endpoint and see if a one of the signing keys matches the kid in the header of the JWT. If none of the signing keys match the incoming kid, an error will be thrown. If we have a match, we will pass the right signing key to express-jwt.
  3. express-jwt will the continue its own logic to validate the signature of the token, the expiration, audience and the issuer.
The steps we will follow in our code are:
  • Create the middleware function to validate the .
  • Enable the use of the middleware in our routes.
You can also write some code to actually save the timesheet to a database. This is our sample implementation (some code is omitted for brevity): 
// set dependencies - code omitted

// Enable CORS - code omitted

// Create middleware for checking the JWT
const checkJwt = jwt({
  // Dynamically provide a signing key based on the kid in the header and the signing keys provided by the JWKS endpoint
  secret: jwksRsa.expressJwtSecret({
    cache: true,
    rateLimit: true,
    jwksRequestsPerMinute: 5,
    jwksUri: `https://{yourDomain}/.well-known/jwks.json`
  }),

  // Validate the audience and the issuer
  audience: '{YOUR_API_IDENTIFIER}', //replace with your API's audience, available at Dashboard > APIs
  issuer: 'https://{yourDomain}/',
  algorithms: [ 'RS256' ]
});

// Enable the use of request body parsing middleware - code omitted

// create timesheets API endpoint - code omitted
app.post('/timesheets', checkJwt, function(req, res){
  var timesheet = req.body;

  // Save the timesheet to the database...

  //send the response
  res.status(201).send(timesheet);
});
// launch the API Server at localhost:8080 - code omitted
If we launch our server now and do an HTTP POST to localhost:8080/timesheets we should get the error message Missing or invalid token (which is perfectly fine since we didn’t send an Access Token in our request). In order to test the working scenario as well we need to:
  • Get an Access Token. For details on how to do so refer to: Get an Access Token.
  • Invoke the API while adding an Authorization header to our request with the value Bearer ACCESS_TOKEN (where ACCESS_TOKEN is the value of the token we retrieved in the first step).

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Step 3. Check the application permissions

In this step we will add to our implementation the ability to check if the application has permissions (or scope) to use our endpoint in order to create a timesheet. In particular we want to ensure that the token has the correct scope, which is batch:upload. In order to do this we will make use of the express-jwt-authz Node.js package, so go ahead and add that to your project: 
npm install express-jwt-authz --save
Now it is as simple as adding a call to jwtAuthz(...) to your middleware to ensure that the JWT contain a particular scope in order to execute a particular endpoint. We will add an additional dependency. The express-jwt-authz library, which is used in conjunction with express-jwt, validates the JWT and ensures it bears the correct permissions to call the desired endpoint. For more information refer to the express-jwt-authz GitHub repository. This is our sample implementation (some code is omitted for brevity): 
// set dependencies - some code omitted
const jwtAuthz = require('express-jwt-authz');

// Enable CORS - code omitted

// Create middleware for checking the JWT - code omitted

// Enable the use of request body parsing middleware - code omitted

// create timesheets API endpoint
app.post('/timesheets', checkJwt, jwtAuthz(['create:timesheets'], { customUserKey: 'auth' }), function(req, res){
  var timesheet = req.body;

  // Save the timesheet to the database...

  //send the response
  res.status(201).send(timesheet);
})

// launch the API Server at localhost:8080 - code omitted
If we invoke our API with a token that does not include this scope we should get the error message Forbidden with the HTTP status code 403. You can test this by removing this scope from your API.

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Step 4. Determine the User Identity

The express-jwt middleware which is used to validate the JWT, also sets the req.auth with the information contained in the JWT. If you want to use the sub claim to identify the user uniquely, you can simply use req.auth.sub. In the case of the timesheets application however, we want to use the email address of the user as the unique identifier. The first thing we need to do is to write a rule which will add the email address of the user to the Access Token. Go to the Rules section of the Dashboard and click on the Create Rule button. You can give the rule a descriptive name, for example Add email to Access Token, and then use the following code for the rule: 
function (user, context, callback) {
  const namespace = 'https://api.exampleco.com/';
  context.accessToken[namespace + 'email'] = user.email;
  callback(null, user, context);
}
The namespace is used to ensure the claim has a unique name and does not clash with the names of any of the standard OIDC claims. However, Auth0 supports namespaced and non-namespaced custom claims. For more info on custom claims, see Create Custom Claims. Next, inside your API, you can retrieve the value of the claim from req.auth, and use that as the unique user identity which you can associate with timesheet entries. 
app.get('/timesheets', checkJwt, jwtAuthz(['read:timesheets'], { customUserKey: 'auth' }), function(req, res) {
  var timesheet = req.body;

  // Associate the timesheet entry with the current user
  var userId = req.auth['https://api.exampleco.com/email'];
  timesheet.user_id = userId;

  // Save the timesheet to the database...

  //send the response
  res.status(201).send(timesheet);
});