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

Hey there, fellow JavaScript developer! Ready to dive into the world of Affinity integrations? Today, we're going to tackle one of the most crucial parts of building a public integration: the authorization flow. Don't worry, it's not as daunting as it sounds. Let's break it down step by step and get you up and running in no time.

Prerequisites

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

• Your favorite JavaScript environment set up
• An Affinity developer account with API credentials
• A basic understanding of OAuth 2.0 (but don't sweat it if you're a bit rusty)

OAuth 2.0 Flow: The Quick and Dirty

We're using the OAuth 2.0 authorization code flow here. In simple terms: your app asks for permission, the user grants it, and you get a special code to exchange for an access token. Easy peasy!

Setting up the Authorization Request

First things first, let's construct that authorization URL:

const authUrl = 'https://auth.affinity.co/oauth/authorize';
const clientId = 'YOUR_CLIENT_ID';
const redirectUri = 'YOUR_REDIRECT_URI';
const state = generateRandomString(); // For security, implement this!

const url = `${authUrl}?client_id=${clientId}&redirect_uri=${redirectUri}&response_type=code&state=${state}`;

Pro tip: That state parameter? It's your friend. Use it to prevent CSRF attacks.

Handling the Redirect

Once the user approves your app, Affinity will redirect them back to you with a code. Let's catch it:

app.get('/callback', (req, res) => {
  const { code, state } = req.query;
  
  // Verify the state matches what you sent
  if (state !== savedState) {
    return res.status(400).send('State mismatch. Possible CSRF attack.');
  }
  
  // Now you've got the code, time to exchange it!
});

Exchanging the Code for an Access Token

Now for the good stuff. Let's trade that code for an access token:

const tokenUrl = 'https://auth.affinity.co/oauth/token';
const response = await fetch(tokenUrl, {
  method: 'POST',
  headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
  body: new URLSearchParams({
    grant_type: 'authorization_code',
    code,
    client_id: clientId,
    client_secret: 'YOUR_CLIENT_SECRET',
    redirect_uri: redirectUri
  })
});

const { access_token, refresh_token } = await response.json();

Storing and Refreshing Tokens

Great job! Now you've got the tokens. Store them securely (please, not in plain text) and remember to refresh when needed:

async function refreshAccessToken(refreshToken) {
  // Similar to the code exchange, but use grant_type: 'refresh_token'
}

Making Authenticated Requests

Time to put that access token to work:

const apiResponse = await fetch('https://api.affinity.co/api/endpoint', {
  headers: {
    'Authorization': `Bearer ${accessToken}`
  }
});

Error Handling and Edge Cases

Things don't always go smoothly, so be prepared:

if (apiResponse.status === 401) {
  // Token might be expired, try refreshing
  const newToken = await refreshAccessToken(refreshToken);
  // Retry the request with the new token
}

Security Considerations

Remember:

• Always use HTTPS
• Store tokens securely (consider encryption at rest)
• Validate the state parameter to prevent CSRF attacks

Testing the Auth Flow

Before you pop the champagne:

1. Test the happy path manually
2. Try some edge cases (expired tokens, invalid codes)
3. Consider setting up automated tests for ongoing peace of mind

Wrapping Up

And there you have it! You've just built a robust auth flow for your Affinity integration. Pat yourself on the back – you've tackled one of the trickiest parts of API integration.

Remember, this is just the beginning. With this solid foundation, you're all set to start building amazing features with the Affinity API. Go forth and integrate!

Happy coding, and don't forget to celebrate your wins along the way. You've got this! 🎉