An example of using the Google API to authenticate.

auth-utils.ts

import { GoogleUserInfo } from '../model/definitions'
import HttpException from '../model/HttpException'
import { Request } from 'express';
import { getEmail } from '../accessor/database.mongo'
const fetch = require('node-fetch')

require('dotenv').config()

const { AUTH_CLIENT_ID, AUTH_CLIENT_SECRET, JWT_SECRET, AUTH_REDIRECT_URI } = process.env;
const SCOPES = ['https://www.googleapis.com/auth/userinfo.email', 'https://www.googleapis.com/auth/userinfo.profile']

const google = require('googleapis').google
const jwt = require('jsonwebtoken')
const OAuth2 = google.auth.OAuth2

const googleEndpoint = (token: string): string => `https://www.googleapis.com/oauth2/v1/userinfo?access_token=${token}`

export const getAuthClient = (): typeof OAuth2 => new OAuth2(AUTH_CLIENT_ID, AUTH_CLIENT_SECRET, AUTH_REDIRECT_URI)

export function verifyJwt(jwt_cookie: string): any {
    return jwt.verify(jwt_cookie, JWT_SECRET);
}

export function generateAuthUrl(oauth2Client: typeof OAuth2 = getAuthClient()): string {
    return oauth2Client.generateAuthUrl({
        access_type: 'offline', // Indicates that we need to be able to access data continously without the user constantly giving us consent
        scope: SCOPES // Using the access scopes from our config file
    });
}

export async function getGoogleUserInfo(request: Request): Promise<GoogleUserInfo> {
    // Check if their is a cookie to read.
    if (!request.cookies.jwt) {
        throw new HttpException(401, "No cookie found")
    }

    // Get creedentials from cookie.
    const oauth2Client = getAuthClient()
    oauth2Client.credentials = verifyJwt(request.cookies.jwt);

    // Extract Google information from token.
    const access_token = oauth2Client.credentials.access_token
    const GoogleResponse = await fetch(googleEndpoint(access_token), { method: 'GET' })
    if (!GoogleResponse) {
        throw new HttpException(GoogleResponse.status, GoogleResponse.statusText)
    }
    return GoogleResponse.json() as Promise<GoogleUserInfo>
}

export async function isAuthorized(request: Request, aliasNeeded: string): Promise<boolean> {
    try {
        // Get user email and needed email.
        const [{ email }, necessaryEmail] = await Promise.all([getGoogleUserInfo(request), getEmail(aliasNeeded)])

        // Check if emails match.
        return email === necessaryEmail
    } catch {
        return false
    }
}