Gmail API service account request- Precondition check failed - node.js

Question

I'm trying to work with the google API's for the first time, and when I attempt to make a request to the gmail API I'm getting a "precondition check failed" error. I am using a service account authorization, not Oauth2 user consent. Things I've tried:
Authorized "domain wide delegation" for the service account.
Ensured the APP is trusted in the G suite account.
Ensured service account role is "owner"
Enabled domain wide delegation for the client ID of the service account in the g suite admin panel.
This is an adapted sample from the Node client library, but the sample did not use service account auth so I wasn't able to use the sample directly.
const path = require('path');
const {google} = require('googleapis');
const gmail = google.gmail('v1');
async function runSample() {
// Obtain user credentials to use for the request
const auth = new google.auth.GoogleAuth({
keyFile: path.resolve(__dirname, 'google-key.json'),
scopes: ['https://www.googleapis.com/auth/gmail.readonly'],
});
google.options({auth});
const res = await gmail.users.messages.list({userId: 'me'}); // have tried with my gsuite email address as well
console.log(res.data);
return res.data;
}
if (module === require.main) {
runSample().catch(console.error);
}
module.exports = runSample;
Returning error with message: Error: Precondition check failed.

Answer 1

After searching the dark web for eternity, I found a link to a github issue that described how to authenticate as a service using JWT auth.
This is a working version of what I was trying to accomplish:
const path = require('path');
const {google} = require('googleapis');
async getMessageList(userId, qty) {
const JWT = google.auth.JWT;
const authClient = new JWT({
keyFile: path.resolve(__dirname, 'google-key.json'),
scopes: ['https://www.googleapis.com/auth/gmail.readonly'],
subject: 'admin#example.com' // google admin email address to impersonate
});
await authClient.authorize(); // once authorized, can do whatever you want
const gmail = google.gmail({
auth: authClient,
version: 'v1'
});
const response = await gmail.users.messages.list({
includeSpamTrash: false,
maxResults: qty,
q: "",
userId: userId
});
// the data object includes a "messages" array of message data
return response.data;
}