How to build a public Sage Business Cloud integration: Building the Auth Flow

Aug 11, 2024 • 7 minute read

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

Introduction

Sage Business Cloud is a powerhouse for businesses, and integrating with it can open up a world of possibilities for your app. But before we can start playing with all that juicy business data, we need to make sure we're doing it securely. That's where our auth flow comes in!

Prerequisites

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

A Sage Developer account (if you don't have one, go grab it!)
An application registered in the Sage Developer Portal
A Node.js environment with Express.js set up

Got all that? Great! Let's get to the good stuff.

OAuth 2.0 Flow Overview

We'll be using the OAuth 2.0 Authorization Code Grant flow. It's like a secret handshake between your app and Sage, ensuring that only the cool kids (your authorized users) get in. The key players in this dance are:

Client ID: Your app's unique identifier
Client Secret: Your app's password (keep it secret, keep it safe!)
Redirect URI: Where Sage sends the user after they've logged in

Implementing the Authorization Flow

Initiating the Auth Request

First things first, let's get that authorization URL set up:

const authUrl = `https://www.sageone.com/oauth2/auth/central?client_id=${clientId}&response_type=code&redirect_uri=${redirectUri}`;

Now, when your user wants to connect their Sage account, just redirect them to this URL. They'll log in to Sage, and if everything checks out, Sage will send them back to your redirect URI with a special code.

Handling the Callback

When the user comes back to your app, they'll bring a shiny new authorization code. Time to trade it in for an access token:

app.get('/callback', async (req, res) => {
  const { code } = req.query;
  
  const tokenResponse = await axios.post('https://oauth.accounting.sage.com/token', {
    grant_type: 'authorization_code',
    client_id: clientId,
    client_secret: clientSecret,
    code,
    redirect_uri: redirectUri
  });

  const { access_token, refresh_token } = tokenResponse.data;
  // Store these tokens securely!
});

Token Management

Now that you've got your tokens, treat them like gold! Store them securely (please, not in plain text) and remember to refresh that access token when it expires:

async function refreshAccessToken(refreshToken) {
  const response = await axios.post('https://oauth.accounting.sage.com/token', {
    grant_type: 'refresh_token',
    client_id: clientId,
    client_secret: clientSecret,
    refresh_token: refreshToken
  });

  return response.data.access_token;
}

Error Handling and Edge Cases

Sometimes things don't go as planned. Be ready to handle:

Invalid or expired tokens (hint: refresh or re-authenticate)
Users saying "no thanks" to your app's permissions request

Graceful error handling will make your users love you even more!

Best Practices

Want to level up your auth game? Here are two pro tips:

Use the state parameter to prevent CSRF attacks:

const state = crypto.randomBytes(16).toString('hex');
// Add state to your auth URL and verify it in the callback

Implement PKCE for extra security (especially great for mobile apps)

Testing the Auth Flow

Time to put on your detective hat! Use tools like Postman to test your flow. Common hiccups include:

Mismatched redirect URIs
Incorrect client ID or secret
Forgetting to URL encode parameters

Don't worry if you hit a snag – debugging is half the fun (right?).

Conclusion

And there you have it! You've just built a rock-solid auth flow for your Sage Business Cloud integration. Remember, the key steps are:

Get the user's permission
Exchange the code for tokens
Use and refresh those tokens like a boss

From here, the sky's the limit. Go forth and integrate!

Additional Resources

Want to dive deeper? Check out:

Happy coding, and may your integrations be ever secure and user-friendly!