Send mail via Google Apps Gmail using service account domain wide delegation in nodejs

Question

I\'ve been reading tutorials and seeing examples for 2 days already, with no success. I want to send an email using Google Apps Gmail account in NodeJS environment, however,

Answer 1

So I was half-step close to the solution, the problem was that while creating const jwtClient = new google.auth.JWT(googleKey.client_email, null, googleKey.private_key, ['https://www.googleapis.com/auth/gmail.send'], null); i did not mention the account to be impersonated.

The correct initialization should be: const jwtClient = new google.auth.JWT(googleKey.client_email, null, googleKey.private_key, ['https://www.googleapis.com/auth/gmail.send'], 'user@domain.com');

To summarize, the correct steps are:

1. Created a project in Google Cloud Platform
2. Created a service account
3. Enabled Domain Wide Delegation for the service account
4. Downloaded the key for the service account in JSON format
5. API Manager > Credentials i have created OAuth 2.0 Client ID
6. Enabled Gmail API for the project

In Google Apps Admin console:

1. In Security > Advanced Settings > Manage API client access i have added the Client ID from step 4 above
2. I have added all possible scopes for the Client ID

This is the code that sends mails:

const google = require('googleapis');
const googleKey = require('./google-services.json');
const jwtClient = new google.auth.JWT(googleKey.client_email, null, googleKey.private_key, ['https://www.googleapis.com/auth/gmail.send'], '<user to impersonate>');

jwtClient.authorize((err, tokens) => {
  if (err) {
    console.err(err);
    return;
  }
  console.log('Google auth success')
  var gmail = google.gmail({version: 'v1'})
  var raw = <build base64 string according to RFC 2822 specification>

  var sendMessage = gmail.users.messages.send({
    auth: jwtClient,
    userId: '<user to impersonate>',
    resource: {
      raw: raw
    }
  }, (err, res) => {
     if (err) {
       console.error(err);
     } else {
       console.log(res);
     }
 });

Hope that would be helpful for others

Answer 2

Thanks very much @agoldis. Both the summary steps and the code were very helpful.

It helped me pick up on a few things I needed to fix on both the GoogleWorkspace and the ApplicationCode end of the communication path. Below is my c# implementation for anyone who needs it.

private static void Try4()
{
  try {
     //file included in project with properties:  CopyToOutputDirectory = CopyAlways
     var credential = GoogleCredential.FromFile("MyPrj-MyServiceAccount-Credentials.json")       
                      .CreateScoped(new[] { GmailService.Scope.GmailSend })
                      .CreateWithUser("WhoIAmImpersonating@bla.com")
                      .UnderlyingCredential as ServiceAccountCredential;

     var service = new GmailService(new BaseClientService.Initializer() { HttpClientInitializer = credential });

     var nl = Environment.NewLine;
     string plainText =         "From:         WhoIAmImpersonating@bla.com" 
                         + nl + "To:           myfriend@gmail.com,"
                         + nl + "Subject:      This is the Subject" 
                         + nl + "Content-Type: text/html; charset=us-ascii" 
                         + nl 
                         + nl + "This is the message text.";
     var newMsg = new Message() { Raw = Base64UrlEncode(plainText) };

     service.Users.Messages.Send(newMsg, "WhoIAmImpersonating@bla.com").Execute();
     Console.WriteLine("Message Sent OK");
  }
  catch (Exception ex) {
      Console.WriteLine("Message failed");
  }
}



private static string Base64UrlEncode(string input)
{
  var inputBytes = System.Text.Encoding.UTF8.GetBytes(input);
  return Convert.ToBase64String(inputBytes)
                .Replace('+', '-')
                .Replace('/', '_')
                .Replace("=", "" );
}