CRON Node.js Gmail API script - node.js

Question

How do I properly setup Gmail API script that sends emails?
I am about to use this method and I started building my script from this quickstart guide.
Is there alternative way to do this without using OAuth 2 validation? Or a way to validate once for all?

Answer 1

Well, in using Gmail APi with your app, you need to use OAuth 2.0 because all request to the Gmail API must be authorized by an authenticated user. And if you notice the quickstart, there is a step here that you need to create a credentials/Outh client ID to make this API work.
For more information, there is another way to authorize your app with Gmail. You can do it with the help of Google+ Sign-in that provide a "sign-in with Google" authentication method for your app.

Answer 2

While asking for authorization from GMail, OAuth 2.0 gives one access token and one refresh token. To avoid validation every time, store the access token. Use the refresh token to get the new access token after it is expired (access token expires every one hour).
Read about this process here: https://developers.google.com/identity/protocols/OAuth2

Answer 3

I found solution using JWT to authorize OAuth2.
You need to have admin account to create Domain wide delegation service account. Then in Developer console you need to download service key JSON file which you load as credentials.
First fetch all users like this: (here you need to use account with admin directory rights)
const google = require('googleapis');
const gmail = google.gmail('v1');
const directory = google.admin('directory_v1');
const scopes = [
'https://www.googleapis.com/auth/gmail.readonly',
'https://www.googleapis.com/auth/admin.directory.user.readonly'
];
const key = require('./service_key.json');
var authClient = new google.auth.JWT(
key.client_email,
key,
key.private_key,
scopes,
"authorized#mail.com"
);
authClient.authorize(function(err, tokens){
if (err) {
console.log(err);
return;
}
directory.users.list(
{
auth: authClient,
customer: 'my_customer',
maxResults: 250,
orderBy: 'email'
}, (err, resp) => {
if (err) {
console.log(err);
return;
}
console.log(resp);
});
});
Then you need to fetch Thread lists (100 per request (page)). And for each thread object you need to call get method for full thread. When using Gmail API authorize as user you want to fetch emails from. In request as userId use value 'me'.