How to generate authentication credentials for Google Sheets API? - google-sheets-api

Question

Step 1 (completed):
As instructed, I have followed every step in Google's Node.js Quickstart:
https://developers.google.com/sheets/api/quickstart/nodejs
and it ran perfectly without any errors. My understanding was that after I run index.js, a token.json is created. After which, I can somehow use the token.json for any future authentication purpose without needing credentials.json every time. Please, correct me if I am wrong in this assumption. I am only making this assumption based on what Google is saying in the previously given link - "Authorization information is stored on the file system, so subsequent executions will not prompt for authorization."
Step 2 (problem):
Below is another code snippet is given by a Google Sheet's API's documentation page for reading multiple range data:
https://developers.google.com/sheets/api/reference/rest/v4/spreadsheets.values/batchGet
I, however, do not know how to generate authentication credentials for authClient. Am I suppose to do something with token.json? If yes, what is the protocol of using the token.json file?
Please feel free to ask any follow-up questions if needed.
enter code here// BEFORE RUNNING:
// ---------------
// 1. If not already done, enable the Google Sheets API
// and check the quota for your project at
// https://console.developers.google.com/apis/api/sheets
// 2. Install the Node.js client library by running
// `npm install googleapis --save`
const {google} = require('googleapis');
var sheets = google.sheets('v4');
authorize(function(authClient) {
var request = {
// The ID of the spreadsheet to retrieve data from.
spreadsheetId: 'my-spreadsheet-id', // TODO: Update placeholder value.
// The A1 notation of the values to retrieve.
ranges: [], // TODO: Update placeholder value.
// How values should be represented in the output.
// The default render option is ValueRenderOption.FORMATTED_VALUE.
valueRenderOption: '', // TODO: Update placeholder value.
// How dates, times, and durations should be represented in the output.
// This is ignored if value_render_option is
// FORMATTED_VALUE.
// The default dateTime render option is [DateTimeRenderOption.SERIAL_NUMBER].
dateTimeRenderOption: '', // TODO: Update placeholder value.
auth: authClient,
};
sheets.spreadsheets.values.batchGet(request, function(err, response) {
if (err) {
console.error(err);
return;
}
// TODO: Change code below to process the `response` object:
console.log(JSON.stringify(response, null, 2));
});
});
function authorize(callback) {
// TODO: Change placeholder below to generate authentication credentials. See
// https://developers.google.com/sheets/quickstart/nodejs#step_3_set_up_the_sample
//
// Authorize using one of the following scopes:
// 'https://www.googleapis.com/auth/drive'
// 'https://www.googleapis.com/auth/drive.file'
// 'https://www.googleapis.com/auth/drive.readonly'
// 'https://www.googleapis.com/auth/spreadsheets'
// 'https://www.googleapis.com/auth/spreadsheets.readonly'
var authClient = null;
if (authClient == null) {
console.log('authentication failed');
return;
}
callback(authClient);
}