Noob’s guide to using any Google API in NodeJs

Google offers multiple services to its users and also offers developers the option to build super cool stuff by integrating these services into their apps using their APIs. You can check the list of all the apis provided by Google here

In this article, I’ll walk you through the initial authentication step for using Google APIs. Lets jump right into it

Creating a project in Google Cloud Console

To generate credentials for Google APIs, we need to create a project in Google Cloud Console. Sign in to Google Cloud Console with your google account and create a new project and follow the below steps:

Step 1: Enabling Google API

In the sidemenu, select APIs and Services -> Library -> Search for the Google API you want to use and enable it

Google offers two basic types of credentials to access their API - API key and oAuth 2

• API key is used when accessing publicly available data like Google Maps
• oAuth 2 is used when accessing private data like a user’s Gmail account or Google drive

Getting oAuth credentials involves setting up an oAuth consent screen. You can skip this step if you’re looking only for API Key authentication

Step 2: Setting up the OAuth Screen

• Inside APIs and Services -> OAuth Consent Screen -> Select User Type. You can External for testing
• On the next screen, enter all the application details
• In Scopes section, click on Add Scopes. Each service offers different levels of permissions (i.e. scope) to client data. You can select the scope as per your project requirements.
• If your application is still in Testing phase and you selected External user type previous step, provide emails of all the users who can access your app
• Check the app summary and click Save

Step 3: Generating Credentials

• oAuth Client ID
  • Again in APIs and Services, open Credentials -> Create Credentials -> oAuth Client ID
  • Select your Application Type and add
    • Authorised Origin - You can use localhost with port no. http://localhost:3000 if your app is not hosted
    • Callback URL - This is the url where Google will send the response after OAuth. Again for locally hosted apps, you can use something like http://localhost:3000/auth/google/callback
• API Key
  • Generating API Key is fairly straight forward. Inside APIs and Services, select Credentials -> Create Credentials -> API Key

Connecting our Node Project to Google API

For connecting to Google API, we’ll use the Node client library - googleapis. Install it in your project using npm i goolgeapis

Now to store the cloud project credentials in your app, install dotenv and create a .env file

• For oAuth2 authentication, add CLIENT_ID, CLIENT_SECRET and CALLBACK_URL in the environment file.
• For API Key auth, just add the API_KEY and skip the next step

Step 1: Creating an oAuth2 client

• In our app, we need to create a Node oAuth2 client using our generated credentials which validates our app as a valid client.

const { google } = require('googleapis');
require('dotenv').config();
const { CLIENT_ID, CLIENT_SECRET, CALLBACK_URL } = process.env;

const oauth2Client = new google.auth.OAuth2(
  CLIENT_ID,
  CLIENT_SECRET,
  CALLBACK_URL
);

• In order to authenticate the users of our app and get consent to access their data, we need to generate a unique url based on our project scope. So this allows our app to make requests to Google apis on behalf of the user.

//This method returns a url where the users can see the oAuth consent screen
function getGoogleAuthURL() {

  // Add all the scopes required by your app in this array. 
  // For example, if the scope needed by your app is /auth/calendar, 
  // add it as https://www.googleapis.com/auth/calendar in the array
  const scope = [
    'https://www.googleapis.com/<scope-that-you-selected-earlier>'
  ];

  return oauth2Client.generateAuthUrl({
    //'offline' mode will return a refresh token which we can save in our database to access the user's data in the future
    access_type: 'offline', 
    scope,
  });
}

• We can now create a separate route to redirect our users to the generated url

app.get('/auth/google', (req, res) => {
  res.redirect(getGoogleAuthURL());
});

• When the user is redirected to the callback route, we can get the user details and save it in our DB and perform any other operation as needed

async function getGoogleUser({ code }) {
  // This will return an object with the access_token and refresh_token
  const { tokens } = await oauth2Client.getToken(code);
  oauth2Client.setCredentials({
    refresh_token: tokens.refresh_token
  });

  // Fetch the user's profile with the access token and bearer
  const googleUser = await axios
    .get(
      `https://www.googleapis.com/oauth2/v1/userinfo?alt=json&access_token=${tokens.access_token}`,
      {
        headers: {
          Authorization: `Bearer ${tokens.id_token}`,
        },
      },
    )
    .then(res => {
      return { data: res.data, refresh_token: tokens.refresh_token };
    })
    .catch(error => {
      throw new Error(error.message);
    });
    return googleUser;
}

app.get('/auth/google/callback', async (req, res) => {
  try {
    const googleUser = await getGoogleUser(req.query);

    //Get user id, email and name from the response
    const { id, email, name } = googleUser.data;

    //You can store this refresh token in your db for future access
    const refreshToken = googleUser.refresh_token;

    //Store the data in DB and redirect to some other page

  } catch(err) {
    //Error handling logic here
  }
})

Step 2: Authenticating API requests

• We can authenticate all of our requests either at the global level or at a service level to avoid dealing with it in every request we send
• For API Key authentication, just replace the oauth2Client with API_KEY

// Global authentication
google.options({
  auth: oauth2Client
});

// Service level authentication - Example with Google Drive service
const drive = google.drive({
  version: 'v2',
  auth: oauth2Client
});

And voila! Our Node app is now authenticated to use Google APIs. You can now easily GET and POST data to any of the Google apis provided you have defined the right scope.

You can checkout endpoints for any of api in Google Api explorer and refer the googleapis documentation here

Thank you! Do let me know in the comments if you have any questions.

Stay healthy, Stay happy, Stay safe. Cheers!