OAuth 2.0 Bulk Email | GCP

To analyze and set up OAuth 2.0 for sending bulk emails with Gmail using GCP, here’s a step-by-step breakdown tailored for a Google Cloud Platform (GCP) engineer, including sample code:

Step 1: Setup Project in GCP

Project Name: gmail-bulk-sending
Project Number: 895054114655
Project ID: gmail-bulk-sending-389112

Ensure you have set up a project in GCP with the necessary Gmail API access enabled.

Enable Gmail API: In your GCP project console, navigate to APIs & Services > Library. Search for Gmail API and enable it.
Create OAuth 2.0 Credentials:
- Go to APIs & Services > Credentials.
- Click on Create Credentials and select OAuth 2.0 Client ID.
- Choose Web Application as the application type.
- Add the redirect URI https://developers.google.com/oauthplayground for testing.

Step 2: OAuth 2.0 Playground

You can use Google's OAuth 2.0 Playground to test the OAuth flow:

Use the following link to generate access tokens for the https://www.googleapis.com/auth/gmail.send scope:
```
https://developers.google.com/oauthplayground/#step2&apisSelect=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fgmail.send
```
Select the Gmail API scope and generate an access token.

Step 3: OAuth 2.0 Configuration

Here’s an example of OAuth 2.0 configuration for client credentials:

{
  "web": {
    "client_id": "YOUR_CLIENT_ID.apps.googleusercontent.com",
    "project_id": "gmail-bulk-sending-389112",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token",
    "client_secret": "YOUR_CLIENT_SECRET",
    "redirect_uris": ["https://developers.google.com/oauthplayground"]
  }
}

Replace YOUR_CLIENT_ID and YOUR_CLIENT_SECRET with your actual OAuth credentials from GCP.

Step 4: Firebase Setup for Bulk Email Automation

If you're using Firebase as a backend, you can initialize the Firebase Admin SDK with the following snippet:

var admin = require("firebase-admin");

var serviceAccount = require("path/to/serviceAccountKey.json");

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://gmail-bulk-sending-389112-default-rtdb.firebaseio.com"
});

Make sure that the serviceAccountKey.json contains your Firebase service account key. It will be used to authenticate your app and interact with Gmail API.

Step 5: Sample Code to Send Emails via Gmail API

Here’s a sample Node.js script using the OAuth 2.0 tokens to send a bulk email:

Install necessary dependencies:
```
npm install googleapis nodemailer
```
Sample script to send an email:

const { google } = require('googleapis');
const nodemailer = require('nodemailer');

// OAuth 2.0 setup
const oAuth2Client = new google.auth.OAuth2(
  'YOUR_CLIENT_ID',
  'YOUR_CLIENT_SECRET',
  'YOUR_REDIRECT_URL'
);

oAuth2Client.setCredentials({
  refresh_token: 'YOUR_REFRESH_TOKEN',
});

async function sendBulkEmails() {
  try {
    const accessToken = await oAuth2Client.getAccessToken();
    const transporter = nodemailer.createTransport({
      service: 'gmail',
      auth: {
        type: 'OAuth2',
        user: 'your-email@gmail.com',
        clientId: 'YOUR_CLIENT_ID',
        clientSecret: 'YOUR_CLIENT_SECRET',
        refreshToken: 'YOUR_REFRESH_TOKEN',
        accessToken: accessToken.token,
      },
    });

    const mailOptions = {
      from: 'you@gmail.com',
      to: 'recipient@example.com',
      subject: 'Sending Bulk Emails via OAuth2',
      text: 'This is an email sent using OAuth2 and Gmail API.',
      html: '<h1>Bulk Email Test</h1>',
    };

    const result = await transporter.sendMail(mailOptions);
    return result;
  } catch (error) {
    console.error('Error sending email:', error);
  }
}

sendBulkEmails().then(result => console.log('Email sent', result))
                 .catch(error => console.log(error));

Step 6: Managing Bulk Email

To avoid running into Gmail's bulk sending limits, you may need to throttle your emails and manage batch sizes accordingly. You could store email queues in Firebase and manage scheduling or batch processing via Cloud Functions or App Engine.

Step 7: Additional Configurations

IAM & Admin: Ensure that service accounts have the necessary permissions for Gmail API.
Rate Limits: Be mindful of Gmail’s sending limits for bulk emails (500 recipients per day for standard Gmail accounts, higher for Workspace).

This step-by-step process ensures that you authenticate with OAuth 2.0, send bulk emails through Gmail API, and integrate Firebase for backend management. Let me know if you'd like further clarification on any of these steps!

DevCEDTeam / CED