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Detailed step-by-step instructions to configure Google Cloud Platform, Google Cloud Functions, and set up OAuth for the Gmail API. The instructions include sample code where necessary.

Step 1: Create a New Project

Go to the Google Cloud Console: https://console.cloud.google.com/
Click on the project dropdown located at the top left corner and select "New Project".
Provide a name for your project and click "Create".

Step 2: Enable APIs

In the Cloud Console, ensure that your newly created project is selected from the project dropdown.
Open the "APIs & Services" section from the left sidebar.
Click on "Library" in the left sidebar to access the API Library.
Search for "Gmail API" in the search bar.
Click on the "Gmail API" result.
On the Gmail API page, click the "Enable" button to enable the API.
Repeat the above steps to enable the "Cloud Functions API".

Step 3: Set Up OAuth Consent Screen

In the Cloud Console, ensure that your project is selected.
Open the "APIs & Services" section from the left sidebar.
Click on "OAuth consent screen" in the left sidebar.
Select "Internal" as the User Type and click "Create".
Fill in the required information such as "App name", "User support email", and "Developer contact information".
Click "Save" to save the consent screen configuration.

Step 4: Add or Remove Scopes

In the Cloud Console, go to the "APIs & Services" section.
Click on "OAuth consent screen" in the left sidebar.
Scroll down to the "Scopes" section and click on the "Add or Remove Scopes" button.
In the "Enter Property name or value" field, search for "Gmail API".
Select the following scopes:
Click "Update" and then "Save and Continue".
Go back to the Dashboard by clicking the "Dashboard" link in the left sidebar.

Step 5: Create OAuth Client ID

In the Cloud Console, go to the "APIs & Services" section.
Click on "Credentials" in the left sidebar.
Click on the "Create Credentials" button and select "OAuth client ID".
Choose "Web application" as the application type.
Provide a name for your OAuth client ID.
Add the authorized redirect URIs. For this tutorial, add https://developers.google.com/oauthplayground as the redirect URI.
Click "Create" to create the OAuth client ID.
Note down the generated Client ID and Client Secret.

Step 6: Update OAuth Playground Settings

Go to the OAuth Playground website: https://developers.google.com/oauthplayground
Click on the settings icon (gear icon) on the top-right corner of the page.
Check the box that says "Use your own OAuth credentials".
Enter your Client ID and Client Secret obtained in the previous step.
Click "Close" to save the settings.

Step 7: Obtain Access Token and Refresh Token

In the OAuth Playground, on the left side, find the list of APIs.
Scroll down and select "Gmail API v1" from the list.
In the list of available scopes, select the desired scopes for your application.
Click on the "Authorize APIs" button.
Go through the authorization flow, granting the necessary permissions to the OAuth Playground.
After authorization, you will be redirected back to the OAuth Playground.
Click on the

"Exchange authorization code for tokens" button.
Note down the generated Access Token and Refresh Token.

Step 8: Configure Google Cloud Functions

Set up a new Google Cloud Function or use an existing one for sending email messages using the Gmail API.
Ensure that the Cloud Function allows unauthenticated invocations.
Set the runtime environment variables for your Cloud Function with the following keys and values:
- CLIENT_ID: Your OAuth Client ID
- CLIENT_SECRET: Your OAuth Client Secret
- REDIRECT_URI: The redirect URI configured for your OAuth client ID (e.g., https://developers.google.com/oauthplayground)
- REFRESH_TOKEN: The Refresh Token obtained in the previous step

Step 9: Configure the Cloud Function Code

Update your Cloud Function code with the provided sample code or make necessary modifications based on your requirements.
The sample code below demonstrates a Cloud Function that sends email messages using the Gmail API:

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

exports.sendEmail = async (req, res) => {
  // Parse the request body
  const body = req.body;
  const recipients = body.recipients;
  const subject = body.subject;
  const message = body.message;

  // Create an OAuth2 client
  const oAuth2Client = new google.auth.OAuth2(
    process.env.CLIENT_ID,
    process.env.CLIENT_SECRET,
    process.env.REDIRECT_URI
  );

  try {
    // Set the credentials using the Refresh Token
    await oAuth2Client.setCredentials({ refresh_token: process.env.REFRESH_TOKEN });

    // Create the Gmail API client
    const gmail = google.gmail({ version: 'v1', auth: oAuth2Client });

    // Construct the email message
    const email = [
      'From: sender@gmail.com',
      `To: ${recipients}`,
      'Subject: ' + subject,
      '',
      message,
    ].join('\n');

    // Send the email
    const response = await gmail.users.messages.send({
      userId: 'me',
      requestBody: {
        raw: Buffer.from(email).toString('base64'),
      },
    });

    console.log(response.data);

    res.sendStatus(200);
  } catch (error) {
    console.error(error);
    res.sendStatus(500);
  }
};

Step 10: Set Maximum Number of Instances (Optional)

If necessary, set the maximum number of instances for your Cloud Function to control concurrency and rate limiting.

Step 11: Test the Functionality

Deploy your Cloud Function and verify that it is running without errors.
Test the functionality by sending HTTP requests to the Cloud Function endpoint or triggering it using scheduled jobs or other event-based triggers.
Check the logs and confirm that email messages are being sent successfully.

By following these detailed step-by-step instructions and using the provided sample code, you should be able to configure Google Cloud Platform, set up OAuth for the Gmail API, and utilize Google Cloud Functions to send email messages using the Gmail API.

DevCEDTeam / CED

Descriptions #24