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

Hey there, fellow JavaScript aficionados! Ready to dive into the world of Circle integrations? Today, we're going to focus on one of the most crucial aspects of building a public integration: the authorization flow. Buckle up, because we're about to make auth both secure and smooth as butter.

Prerequisites

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

• Node.js installed (you knew that was coming, right?)
• Your favorite code editor
• Circle API credentials (if you don't have these yet, hop over to the Circle developer portal and grab 'em)

Setting up the project

Let's kick things off by setting up our project:

mkdir circle-integration && cd circle-integration
npm init -y
npm install express axios dotenv

Create a .env file in your project root and add your Circle API credentials:

CIRCLE_CLIENT_ID=your_client_id
CIRCLE_CLIENT_SECRET=your_client_secret
CIRCLE_REDIRECT_URI=http://localhost:3000/callback

Implementing OAuth 2.0 flow

Now for the fun part! Let's implement the OAuth 2.0 flow:

const express = require('express');
const axios = require('axios');
require('dotenv').config();

const app = express();

app.get('/auth', (req, res) => {
  const authUrl = `https://auth.circle.com/oauth2/authorize?client_id=${process.env.CIRCLE_CLIENT_ID}&redirect_uri=${process.env.CIRCLE_REDIRECT_URI}&response_type=code`;
  res.redirect(authUrl);
});

app.get('/callback', async (req, res) => {
  const { code } = req.query;
  try {
    const response = await axios.post('https://auth.circle.com/oauth2/token', {
      grant_type: 'authorization_code',
      code,
      client_id: process.env.CIRCLE_CLIENT_ID,
      client_secret: process.env.CIRCLE_CLIENT_SECRET,
      redirect_uri: process.env.CIRCLE_REDIRECT_URI
    });
    const { access_token, refresh_token } = response.data;
    // Store these tokens securely (more on this later)
    res.send('Authorization successful!');
  } catch (error) {
    res.status(500).send('Authorization failed');
  }
});

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

Storing and managing access tokens

Alright, we've got our tokens. Now let's keep 'em safe and fresh:

const tokens = {
  access_token: null,
  refresh_token: null,
  expires_at: null
};

function storeTokens(access_token, refresh_token, expires_in) {
  tokens.access_token = access_token;
  tokens.refresh_token = refresh_token;
  tokens.expires_at = Date.now() + expires_in * 1000;
}

async function refreshAccessToken() {
  try {
    const response = await axios.post('https://auth.circle.com/oauth2/token', {
      grant_type: 'refresh_token',
      refresh_token: tokens.refresh_token,
      client_id: process.env.CIRCLE_CLIENT_ID,
      client_secret: process.env.CIRCLE_CLIENT_SECRET
    });
    storeTokens(response.data.access_token, response.data.refresh_token, response.data.expires_in);
  } catch (error) {
    console.error('Failed to refresh token:', error);
  }
}

Making authenticated requests to Circle API

Time to put those tokens to work:

async function makeCircleApiRequest(endpoint, method = 'GET', data = null) {
  if (Date.now() >= tokens.expires_at) {
    await refreshAccessToken();
  }

  try {
    const response = await axios({
      method,
      url: `https://api.circle.com/v1/${endpoint}`,
      headers: {
        Authorization: `Bearer ${tokens.access_token}`
      },
      data
    });
    return response.data;
  } catch (error) {
    console.error('API request failed:', error);
    throw error;
  }
}

Error handling and edge cases

Let's not forget about those pesky errors:

function handleAuthError(error) {
  if (error.response && error.response.status === 401) {
    console.log('Unauthorized. Refreshing token...');
    return refreshAccessToken();
  }
  console.error('Authentication error:', error);
  throw error;
}

Best practices and security considerations

Remember, folks: security isn't just a feature, it's a lifestyle. Here are some quick tips:

• Use HTTPS in production
• Implement PKCE for added security
• Never expose your client secret on the client-side
• Regularly rotate your refresh tokens

Testing the auth flow

Last but not least, let's make sure everything's working as smooth as a well-oiled machine:

async function testAuthFlow() {
  try {
    const userInfo = await makeCircleApiRequest('user');
    console.log('User info:', userInfo);
  } catch (error) {
    console.error('Test failed:', error);
  }
}

testAuthFlow();

Wrapping up

And there you have it! You've just built a rock-solid auth flow for your Circle integration. Remember, this is just the beginning. From here, you can start building out the rest of your integration, adding more API calls, and creating an awesome user experience.

Keep coding, keep learning, and most importantly, keep having fun with it. Until next time, happy integrating!