How to build a public GitLab integration: Building the Auth Flow

Aug 2, 2024 • 7 minute read

Hey there, fellow JavaScript enthusiast! Ready to dive into the world of GitLab integrations? Today, we're going to tackle one of the most crucial parts of building a public GitLab integration: the authorization flow. Buckle up, because we're about to make your integration secure and user-friendly in no time!

Introduction

GitLab integrations are a fantastic way to extend the functionality of your apps and services. But before we can start pulling repositories or creating issues, we need to make sure our users can securely authorize our app to access their GitLab accounts. That's where the auth flow comes in, and trust me, it's not as scary as it sounds!

Prerequisites

Before we jump in, make sure you've got:

A GitLab account and an application set up in GitLab's developer settings
Node.js installed on your machine
Basic knowledge of Express.js (we'll be using it for our server)
Your favorite code editor ready to go

Got all that? Great! Let's get started.

OAuth 2.0 Flow Overview

We'll be using OAuth 2.0's authorization code grant flow. Don't worry if that sounds like a mouthful – it's just a secure way for users to grant our app access to their GitLab data without sharing their passwords. Neat, right?

Setting up the Server

First things first, let's set up a basic Express server:

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

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

Don't forget to set up your environment variables for your client ID and secret. Keep these safe – they're the keys to your integration kingdom!

Implementing the Authorization Flow

Redirect to GitLab's authorization page

When a user wants to connect their GitLab account, we'll redirect them to GitLab's authorization page. Here's how:

app.get('/auth', (req, res) => {
  const authUrl = `https://gitlab.com/oauth/authorize?client_id=${process.env.CLIENT_ID}&redirect_uri=${encodeURIComponent(process.env.REDIRECT_URI)}&response_type=code&scope=api`;
  res.redirect(authUrl);
});

Handling the callback

After the user authorizes your app, GitLab will redirect them back to your specified callback URL with an authorization code. Let's set up a route to handle that:

app.get('/callback', async (req, res) => {
  const { code } = req.query;
  // We'll use this code in the next step
});

Exchanging the code for an access token

Now for the exciting part – turning that code into an access token:

const axios = require('axios');

// Inside your callback route
const tokenResponse = await axios.post('https://gitlab.com/oauth/token', {
  client_id: process.env.CLIENT_ID,
  client_secret: process.env.CLIENT_SECRET,
  code,
  grant_type: 'authorization_code',
  redirect_uri: process.env.REDIRECT_URI
});

const accessToken = tokenResponse.data.access_token;
// Store this token securely - we'll need it for API requests!

Using the Access Token

With your shiny new access token, you can now make authenticated requests to the GitLab API. Here's a quick example:

const getUserProjects = async (accessToken) => {
  const response = await axios.get('https://gitlab.com/api/v4/projects', {
    headers: { Authorization: `Bearer ${accessToken}` }
  });
  return response.data;
};

Remember to handle token expiration and refresh – your users will thank you!

Error Handling and Security Considerations

Always validate the state parameter to prevent CSRF attacks, store tokens securely (consider encryption at rest), and please, please use HTTPS in production. Security isn't just a feature; it's a necessity!

Testing the Integration

Before you pop the champagne, make sure to thoroughly test your integration. Try the happy path, but also test error scenarios. Consider setting up automated tests to catch any future regressions.

Conclusion

And there you have it! You've just built a secure authorization flow for your GitLab integration. Pat yourself on the back – you've taken a big step towards creating a powerful, user-friendly integration.

Remember, this is just the beginning. From here, you can expand your integration to do all sorts of cool things with GitLab's API. The sky's the limit!

Additional Resources

Want to dive deeper? Check out:

Now go forth and integrate! Your users are waiting for the awesome features you're about to build. Happy coding!