server.js

const fs = require('fs');
const path = require("path");
const readline = require('readline');

const express = require("express");
const {google} = require('googleapis');

const app = express();
const port = 3000;

// If modifying these scopes, delete token.json.
const SCOPES = [
  'https://www.googleapis.com/auth/classroom.courses.readonly',
  'https://www.googleapis.com/auth/classroom.profile.photos',
  'https://www.googleapis.com/auth/classroom.rosters.readonly',
];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = 'token.json';

const streetAcademyId = '15075960905';
const testClassId = '40854525995';

let creds;

app.get("/", (req, res) => res.sendFile(path.join(__dirname, "./index.html")));

app.get("/courses", (req, res) => {
  authorize(creds, (auth) => {
    const classroom = google.classroom({version: 'v1', auth});
    classroom.courses.list({
      pageSize: 10,
    }, (err, gcres) => {
      if(err) { return console.error('The API returned an error: ' + err); }

      const courses = gcres.data.courses.map(course => {
        return {
          name: course.name,
          id: course.id,
          url: course.alternateLink,
          state: course.courseState
        };
      });

      res.json(courses);
    });
  });
});

app.get("/photos", (req, res) => {
  authorize(creds, (auth) => {
    const classroom = google.classroom({version: 'v1', auth});
    classroom.courses.students.list({
      pageSize: 0,
      courseId: req.query.course_id
    }, (err, gcres) => {
      if (err) return console.error('The API returned an error: ' + err + err.code);
      const students = gcres.data.students.map(student => {
        return { name: student.profile.name.fullName, photo: student.profile.photoUrl };
      });
      res.json(students)
    });
  });
});

fs.readFile('credentials.json', (err, content) => {
  if(err) { console.warn('Error loading client secret file:', err); }
  else { creds = JSON.parse(content); }

  app.listen(port, () => console.log(`Listening on port ${port}!`));
});



/**
 * Create an OAuth2 client with the given credentials, and then execute the
 * given callback function.
 * @param {Object} credentials The authorization client credentials.
 * @param {function} callback The callback to call with the authorized client.
 */
function authorize(credentials, callback) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getNewToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}

/**
 * Get and store new token after prompting for user authorization, and then
 * execute the given callback with the authorized OAuth2 client.
 * @param {google.auth.OAuth2} oAuth2Client The OAuth2 client to get token for.
 * @param {getEventsCallback} callback The callback for the authorized client.
 */
function getNewToken(oAuth2Client, callback) {
  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();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) return console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}