Firebase Admin NodeJS API Example

A Node.js REST API example that uses Firebase Admin, built with Express and Typescript that can be used as template for the creation of new servers.

The main aspects of this sample are:

• A project structure that fits well for new API projects that uses Firebase Authentication and Firestore
• Access Control: Restricting routes access with custom claims and checking nuances
• Reject a request outside the controller easily by throwing new HttpResponseError(status, codeString, message)
• Logs: winston module is preconfigured to write .log files

Getting Started

Step 1 -Configure the Firebase Console

In the Firebase Console

Go to Build > Authentication > Get Started > Sign-in method > Email/Password and enable Email/Password and save it.

Also go to Build > Firestore Database > Create database. You can choose the option Start in test mode.

Step 2 - Generate your firebase-credentials.json file

1. Go to your Firebase Project
2. Click on the engine icon (on right of "Project Overview")
3. "Project Settings"
4. "Service Accounts"
5. "Firebase Admin SDK" and make sure the "Node.js" option is selected
6. Click on "Generate new private key". Rename the downloaded file to firebase-credentials.json and move it to inside the environment folder.

⚠️ Keep firebase-credentials.json and environment.ts local, don't commit these files, keep both on .gitignore

As any Firebase server, the API has administrative privileges, that means the API has full permission to perform changes on the Firestore Database (and other Firebase Resources) regardless of how the Firestore Security Rules are configured.

Step 3 - To test your server locally:

This command will start and restart your server as code changes are made, do not use on production

npm run dev

Let's run npm install to install the dependencies and npm run dev to start your server locally on port 3000.

Other commands for the production environment

To build your server:

npm run build

To start your server

npm run start

Step 4 - Use Postman to test it

1. In the Firebase Console > Go to Project Overview and Click on the Web platform to Add a new Platform

2. Add a Nickname like "Postman" and click on Register App

3. Copy the apiKey field

4. Import the postman_collection.json file to your Postman

5. Test creating an account first, after that, go to the Login request example and pass the apiKey as query parameter

6. Copy the idToken and pass it as header for the other requests, the header name is Authorization.

Authentication

Firebase Authentication is used to verify if the client is authenticated on Firebase Authentication, to do so, the client side should inform the Authorization header:

Authorization Header

The client's ID Token on Firebase Authentication in the format Bearer <idToken>, it can be obtained on the client side after the authentication is performed with the Firebase Authentication library for the client side. It can be generated by the client side only.

Option 1: Generating ID Token with Postman:

Follow the previous instructions on Step 4 - Use Postman to test it and pass it as Authorization header value in the format Bearer <idToken>

Option 2: Generating ID Token with a Flutter Client:

final idToken = await FirebaseAuth.instance.currentUser!.getIdToken();
// use idToken as `Authorization` header value in the format "Bearer <idToken>"

Option 3: Generating ID Token with a Web Client:

const idToken = await getAuth(firebaseApp).currentUser?.getIdToken();
// use idToken as `Authorization` header value in the format "Bearer <idToken>"

Access Control

This project uses custom claims on Firebase Authentication to define which routes the users have access to.

Define custom claims to a user

This can be done in the server like below:

await admin.auth().setCustomUserClaims(user.uid, {
    storeOwner: true,
    buyer: false
});

Configuring the routes

You can set a param (array of strings) on the httpServer.<method> function, like:

httpServer.get (
    '/product/:productId/full-details', 
    this.getProductByIdFull.bind(this), ['storeOwner']
);

In the example above, only users with the storeOwner custom claim will have access to the /product/:productId/full-details path.

Is this enough? Not always, so let's check the next section Errors and permissions.

Errors and permissions

You can easily send an HTTP response with code between 400 and 500 to the client by simply throwing a new HttpResponseError(...) on your controller, service or repository, for example:

throw new HttpResponseError(400, 'BAD_REQUEST', "Missing 'name' field on the body");

Sometimes defining roles isn't enough to ensure that a user can't access or modify a specific data, let's imagine if a store owner tries to get full details of a product he is not selling, like a product of another store owner, he still has access to the route because of his storeOwner custom claim, but an additional verification is needed.

if (product.storeOwnerUid != req.auth!.uid) {
    throw new HttpResponseError(
        403, 
        'FORBIDDEN', 
        `Even though you are a store owner,
        you are a owner of another store,
        so you can't see full details of this product`
    );
}

🚫 Permission errors

• "Only storeOwner can access"

Means you are not logged with a buyer claim rather than with a user that contains the storeOwner claim.

• "You aren't the correct storeOwner"

Means you are logged with the correct claim, but you are trying to read others storeOwner's data.

• "Requires authentication"

Authentication fields on Express Request Handler

This project adds 3 new fields to the request object on the express request handler, you can also customize this on src/@types/express.d.ts TypeScript file.

req.authenticated

type: boolean

Is true only if the client is authenticated, which means, the client informed Authorization on the headers, and these values were successfully validated.

req.auth

type: UserRecord | null

If authenticated: Contains user data of Firebase Authentication.

req.token

type: DecodedIdToken | null

If authenticated: Contains token data of Firebase Authentication.

Logs

You can save logs into a file by importing these functions of the src/utils/logger.ts file and using like:

log("this is a info", "info");
logDebug("this is a debug");
logInfo("this is a info");
logWarn("this is a warn");
logError("this is a error");

By default, a logs folder will be generated aside this project folder, in this structure:

- /api-example-firebase-nodejs
--- /node_modules/*
--- /src/*
--- (and more)

- /logs
--- /api-example-firebase-nodejs
------ 2022-8-21.log
------ 2022-8-22.log
------ 2022-8-23.log
------ (and more)

Each .log file contains the logs of the respective day.

You can also go to src/utils/logger.ts and check logsFilename and logsPathAndFilename fields to change the default path and filename so the logs can be saved with a different filename and in a different location.

By default, regardless of the log level, all logs will be saved in the same file, you can also change this behavior on the winston.createLogger(transports: ...) line of the src/utils/logger.ts file.

Getting in touch

Feel free to open a GitHub issue about:

• ❔ questions

• 💡 suggestions

• 🐜 potential bugs

License

MIT

Reference

This project used as reference part of the structure of the GitHub project node-typescript-restify. Thank you developer!

Contacting me

📧 rodrigo@wisetap.com