Bypassing CORS with a Server-Side API Proxy

const express = require('express');
const axios = require('axios'); // Or node-fetch, or any HTTP client library
const cors = require('cors'); // For allowing client requests to YOUR proxy

const app = express();
const PORT = process.env.PORT || 3001;

// Enable CORS for your client application to access this proxy
// In production, configure this more strictly, e.g., `origin: 'https://your-frontend-domain.com'`
app.use(cors());

// Middleware to parse JSON request bodies
app.use(express.json());

// Define a proxy endpoint for a specific external API
// Example: Proxying requests to a public API like JSONPlaceholder
app.get('/api/proxy/jsonplaceholder/:resource', async (req, res) => {
  const { resource } = req.params; // e.g., 'posts', 'users'
  const externalApiUrl = `https://jsonplaceholder.typicode.com/${resource}`;

  try {
    const response = await axios.get(externalApiUrl, { params: req.query });
    res.status(response.status).json(response.data);
  } catch (error) {
    console.error(`Error proxying request to ${externalApiUrl}:`, error.message);
    res.status(error.response?.status || 500).json({ error: 'Failed to fetch data from external API.' });
  }
});

// Example for a POST request proxy
app.post('/api/proxy/my-external-service/:endpoint', async (req, res) => {
  const { endpoint } = req.params;
  const externalApiUrl = `https://api.myexternalservice.com/${endpoint}`;
  const requestBody = req.body;

  try {
    const response = await axios.post(externalApiUrl, requestBody, {
      // Optionally forward headers from client if needed, e.g., Authorization
      // headers: { 'X-Custom-Header': req.headers['x-custom-header'] }
    });
    res.status(response.status).json(response.data);
  } catch (error) {
    console.error(`Error proxying POST request to ${externalApiUrl}:`, error.message);
    res.status(error.response?.status || 500).json({ error: 'Failed to post data to external API.' });
  }
});

app.listen(PORT, () => {
  console.log(`Proxy server listening on port ${PORT}`);
});

// --- Client-Side Usage Example ---
/*
// Assuming your proxy server is running on http://localhost:3001
async function fetchPostsFromProxy() {
  try {
    const response = await fetch('http://localhost:3001/api/proxy/jsonplaceholder/posts');
    const data = await response.json();
    console.log('Posts fetched via proxy:', data);
  } catch (error) {
    console.error('Error fetching posts via proxy:', error);
  }
}

// (async () => {
//   await fetchPostsFromProxy();
// })();
*/