Server Apps + API: Node.js Implementation for the API

This document is part of the Server + 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.

Full source code for the Node.js API implementation can be found in this GitHub repository.

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

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"
}

Next, we need to set our dependencies. We will use the following modules:

• express: This module adds the Express web application framework.

• 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 JWT 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 express-jwt jwks-rsa body-parser --save

Navigate to your API directory and create a server.js file. Your code needs to:

• Set the dependencies.

• Enable the request body parsing middleware.

• Implement the endpoint.

• Launch the API server.

This is our sample implementation:

// set dependencies
const express = require('express');
const app = express();
const jwt = require('express-jwt');
const jwksRsa = require('jwks-rsa');
const bodyParser = require('body-parser');

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

// create timesheets upload API endpoint
app.post('/timesheets/upload', function(req, res){
  res.status(201).send({message: "This is the POST /timesheets/upload 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/upload. You should see a JSON response with a message This is the POST /timesheets/upload endpoint.

So now we have our endpoint but anyone can call it. Continue to the next paragraph to see how we can fix this.

In order to validate our token we will use the jwt function, provided by the express-jwt middleware, and the jwks-rsa package to retrieve the public key from Auth0. 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 Access Token.

• Enable the use of the middleware in our routes.

This is also a good time for you to implement the logic to save the timesheet entries to a local database, or whatever other storage mechanism you may prefer. This is our sample implementation (some code is omitted for brevity):

// set dependencies - code omitted

// enable the use of request body parsing middleware - 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: process.env.AUTH0_AUDIENCE,
  issuer: `https://{yourDomain}/`,
  algorithms: ['RS256']
});

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

  // Save the timesheet entry 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/upload 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).

In this step we will add to our implementation the ability to check if the client has permissions (or scope) to use our endpoint in order to upload 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. This is our sample implementation (some code is omitted for brevity):

// set dependencies - some code omitted
const jwtAuthz = require('express-jwt-authz');

// Create middleware for checking the JWT

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

// Batch upload endpoint
app.post('/timesheets/upload', checkJwt, jwtAuthz(['batch:upload']), function(req, res){
  var timesheet = req.body;

  // Save the timesheet entry 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.

That's it! You are done!