How to get a one-time access token from Google

google-onetime-oauth-cli.js

const TOKEN_PATH = 'token.json';
const SCOPES = ['https://www.googleapis.com/auth/spreadsheets'];
const gapi = require('googleapis');
const clientSecret = process.env.GOOGLE_CLIENT_SECRET;
const clientId = process.env.GOOGLE_CLIENT_ID;
const redirectUri = process.env.GOOGLE_REDIRECT_URI;
const oAuth2Client = new gapi.google.auth.OAuth2(clientId, clientSecret, redirectUri);

const fs = require('fs').promises;
    
function start() {
    // Check if we have previously stored a token.
    return fs.readFile(TOKEN_PATH, 'utf8')
        .then(token => {
            oAuth2Client.setCredentials(JSON.parse(token).tokens);
            console.log("Already authorized.");
            return;
        })
        .catch(err => {
            const authUrl = oAuth2Client.generateAuthUrl({
              access_type: 'offline',
              scope: SCOPES,
            });  
            console.log('Authorize this app by visiting this url:', authUrl);
            const rl = readline.createInterface({
                input: process.stdin,
                output: process.stdout,
            });
            rl.question('Enter the code from that page here: ', (code) => {
                rl.close();
                return oAuth2Client.getToken(code)
                    .then(token => {
                        oAuth2Client.setCredentials(token);
                        // Store the token to disk for later program executions
                        return fs.writeFile(TOKEN_PATH, JSON.stringify(token))
                    })
                    .then(() => {
                        console.log('Token stored to', TOKEN_PATH);
                        return console.log("Authorized.")
                    })
                    .catch((err) => {
                        return console.error('Error while trying to retrieve access token', err);
                    });
            });
    });
}

google-onetime-oauth-web.js

const TOKEN_PATH = 'token.json';
const SCOPES = ['https://www.googleapis.com/auth/spreadsheets'];
const gapi = require('googleapis');
const clientSecret = process.env.GOOGLE_CLIENT_SECRET;
const clientId = process.env.GOOGLE_CLIENT_ID;
const redirectUri = process.env.GOOGLE_REDIRECT_URI;
const oAuth2Client = new gapi.google.auth.OAuth2(clientId, clientSecret, redirectUri);

const fs = require('fs').promises;
    
router.get('/auth/google/start', async (req, res, next) => {
    // Check if we have previously stored a token.
    return fs.readFile(TOKEN_PATH, 'utf8')
        .then(token => {
            oAuth2Client.setCredentials(JSON.parse(token).tokens);
            return res.end("Already authorized.");
        })
        .catch(err => {
            const authUrl = oAuth2Client.generateAuthUrl({
              access_type: 'offline',
              scope: SCOPES,
            });
            return res.redirect(authUrl);
        });
});

router.get('/auth/google/callback', async (req, res, next) => {
    const code = req.query.code;
    return oAuth2Client.getToken(code)
        .then(token => {
            oAuth2Client.setCredentials(token);
            // Store the token to disk for later program executions
            return fs.writeFile(TOKEN_PATH, JSON.stringify(token))
        })
        .then(() => {
            console.log('Token stored to', TOKEN_PATH);
            return res.end("Authorized.")
         })
        .catch((err) => {
            return console.error('Error while trying to retrieve access token', err);
        });
});