Understanding OAuth 2.0 with the help of AI
Tags: oauth, authentication, security, webdev
Published: 2023-08-04 08:44:31


---
title: Understanding OAuth 2.0 with the help of AI
published: true
description: A comprehensive guide to understanding OAuth 2.0, its workflows, and its usage in popular services, aided by AI (ChatGPT).
tags: oauth, authentication, security, webdev
---

Recently, I started using OAuth 2.0 in my work. I found that I didn't fully understand the specifics, so I asked AI (ChatGPT) to explain it to me. I would like to share what I learned.

## Table of Contents
1. [What is OAuth 2.0?](#what-is-oauth)
2. [The OAuth 2.0 Flow](#oauth-flow)
3. [Explaining OAuth 2.0 in a way even a child could understand](#oauth-child)
4. [Famous services using OAuth 2.0](#famous-services)
5. [An example of OAuth 2.0](#example)
6. [Summary](#summary)

## What is OAuth 2.0? <a name="what-is-oauth"></a>

OAuth 2.0 (Open Authorization version 2.0) is an open authentication protocol that allows third-party applications to access services on behalf of the user, without the user having to provide their account information directly. It's a common method for integrating with other applications by sharing some information.

## The OAuth 2.0 Flow <a name="oauth-flow"></a>

The OAuth 2.0 flow is as follows:

1. **Authorization Request**: The user is redirected from the application to the authorization server.
2. **Authorization**: The user logs in to the authorization server and grants access to the resources requested by the client.
3. **Authorization Response**: The authorization server redirects the user back to the client's redirect URI, which includes an authorization code.
4. **Access Token Request**: The client uses the authorization code to request an access token from the authorization server.
5. **Access Token Response**: The authorization server provides the client with an access token. The client uses this token to access the user's data from the resource server.
6. **Resource Request and Response**: The client uses the access token to request resources from the resource server. The resource server verifies the access token and provides the requested resources.

## Explaining OAuth 2.0 in a way even a child could understand <a name="oauth-child"></a>

1. **Ordering Ice Cream**: You (the user) ask your friend (the application) to get ice cream (the data) through your mom (Google or Facebook).
2. **Asking Mom**: Your friend (the application) asks your mom (Google or Facebook) for permission to get ice cream (the data).
3. **Getting an Ice Cream Coupon**: Mom gives your friend (the application) an ice cream coupon (the authorization code).
4. **Exchanging the Coupon for Ice Cream**: Your friend (the application) uses the ice cream coupon (the authorization code) to get the ice cream (user data) from the ice cream shop (the resource server).
5. **Getting the Ice Cream**: The ice cream shop (the resource server) verifies the ice cream coupon (the access token) and gives the ice cream (the data) to your friend (the application).

## Famous services using OAuth 2.0 <a name="famous-services"></a>

OAuth 2.0 is widely used in many famous websites and applications, including Google, Facebook, Twitter, and GitHub.

## An example of OAuth 2.0 <a name="example"></a>

Here's a simple example of OAuth 2.0 using Node.js and Express:

```javascript
const express = require('express');
const request = require('request');
const querystring = require('querystring');

const app = express();

app.get('/login', function(req, res) {
  res.redirect('https://authorize.url?' +
    querystring.stringify({
      response_type: 'code',
      client_id: 'client_id',
      redirect_uri: 'http://localhost:8888/callback',
      scope: 'user-read-private user-read-email'
    }));
});

app.get('/callback', function(req, res) {
  const code = req.query.code || null;
  const authOptions = {
    url: 'https://api.token.url',
    form: {
      code: code,
      redirect_uri: 'http://localhost:8888/callback',
      grant_type: 'authorization_code',
      client_id: 'client_id',
      client_secret: 'client_secret'
    },
    json: true
  };

  request.post(authOptions, function(error, response, body) {
    if (!error && response.statusCode === 200) {
      const access_token = body.access_token;
      res.redirect('/#' +
        querystring.stringify({
          access_token: access_token
        }));
    } else {
      res.redirect('/#' +
        querystring.stringify({
          error: 'invalid_token'
        }));
    }
  });
});

console.log('Listening on 8888');
app.listen(8888);
```

In this code, the user is first redirected to the authorization server by accessing the `/login` endpoint. The redirect response from the authorization server is sent to the `/callback` endpoint, where the access token is requested.

## Summary <a name="summary"></a>

OAuth 2.0 is a common method for third-party applications to access services on behalf of a user without the user having to provide their account information directly. In this article, we've gone through the basic flow and provided a sample code. Now you should have a better understanding of how OAuth 2.0 works.
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