How to Build a Public Square Integration: Building the Auth Flow

Aug 1, 2024 • 6 minute read

Hey there, fellow JavaScript aficionado! Ready to dive into the world of Square integrations? Let's roll up our sleeves and build an auth flow that'll make your users feel like they're gliding through silk. We'll keep things snappy, so buckle up!

Prerequisites

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

A Square Developer account (if not, go grab one!)
Node.js and npm installed on your machine
A basic grasp of OAuth 2.0 (don't worry, we'll refresh your memory)

Setting Up Your Project

First things first, let's get your project off the ground:

Head over to the Square Developer Dashboard and create a new application.
Snag your application ID and secret – you'll need these bad boys soon.
Fire up a new Express.js server. Nothing fancy, just the basics.

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

app.listen(3000, () => console.log('Server running on port 3000'));

Implementing the OAuth 2.0 Flow

Step 1: The Grand Redirect

Time to send your users on a little adventure to Square's Authorization page:

app.get('/auth', (req, res) => {
  const authUrl = `https://connect.squareup.com/oauth2/authorize?client_id=${YOUR_APP_ID}&scope=MERCHANT_PROFILE_READ PAYMENTS_WRITE&state=${generateRandomState()}`;
  res.redirect(authUrl);
});

Pro tip: Always use that state parameter. It's your shield against CSRF attacks!

Step 2: Handling the Callback

Square's sending your users back with a shiny authorization code. Let's trade it for an access token:

app.get('/callback', async (req, res) => {
  const { code, state } = req.query;
  // Verify state to prevent CSRF attacks
  
  const response = await fetch('https://connect.squareup.com/oauth2/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      client_id: YOUR_APP_ID,
      client_secret: YOUR_APP_SECRET,
      code,
      grant_type: 'authorization_code'
    })
  });

  const { access_token, refresh_token } = await response.json();
  // Store these tokens securely!
});

Step 3: Token Management

Now that you've got the goods, store them safely! Consider using encrypted storage or a secure database. And don't forget to set up a refresh mechanism – those access tokens don't last forever!

Making Authenticated Requests

With your shiny new access token, you're ready to rock the Square API:

const fetchMerchantInfo = async (accessToken) => {
  const response = await fetch('https://connect.squareup.com/v2/merchants/me', {
    headers: { 'Authorization': `Bearer ${accessToken}` }
  });
  return response.json();
};

Error Handling and Edge Cases

Always be prepared! Handle token expiration gracefully, and don't forget about those pesky user denials. A smooth error handling flow can make or break your user experience.

Security Considerations

Security isn't just a feature, it's a lifestyle:

Always use HTTPS. No exceptions!
That state parameter? Use it every single time.
Treat tokens like crown jewels. Encrypt, salt, and pepper to taste.

Testing Your Integration

Before you pop the champagne, give your integration a thorough workout in Square's sandbox environment. It's like a dress rehearsal before the big show!

Conclusion

And there you have it! You've just built a rock-solid auth flow for your Square integration. Pat yourself on the back – you've earned it! Remember, this is just the beginning. There's a whole world of Square APIs out there waiting for you to explore.

Additional Resources

Still hungry for more? Check out:

Now go forth and integrate! Your users will thank you for this smooth-as-butter auth flow. Happy coding!