Implement a Basic Node.js API Proxy Gateway

const express = require('express');
const axios = require('axios'); // For making HTTP requests to the target API
const cors = require('cors'); // If your frontend is on a different origin

const app = express();
const port = 3001;

// Configuration for the target API
const TARGET_API_BASE_URL = 'https://jsonplaceholder.typicode.com'; // Example public API
const API_KEY = process.env.TARGET_API_KEY || 'your_secret_api_key'; // For authenticating with target API

// Optional: Enable CORS for your proxy if frontend is on a different origin
app.use(cors());

// Middleware to add/modify headers for the target API (e.g., API Key)
app.use('/api/*', (req, res, next) => {
    // Example: Add an API key to the request to the target API
    req.headers['X-API-Key'] = API_KEY;
    // Example: Remove sensitive headers that shouldn't be passed upstream
    delete req.headers['cookie'];
    delete req.headers['authorization']; // If auth is handled by the proxy
    next();
});

// Proxy endpoint for /api/posts
app.get('/api/posts', async (req, res) => {
    try {
        const response = await axios.get(`${TARGET_API_BASE_URL}/posts`, { headers: req.headers });
        res.json(response.data);
    } catch (error) {
        console.error('Error proxying posts API:', error.message);
        res.status(error.response?.status || 500).json({ error: 'Failed to fetch posts from target API.' });
    }
});

// Generic proxy for any path under /api/v1/*
// Note: This is a basic example, for robust API Gateway features consider libraries like http-proxy-middleware
app.all('/api/v1/*', async (req, res) => {
    const targetPath = req.originalUrl.replace('/api/v1', ''); // Remove proxy prefix
    const targetUrl = `${TARGET_API_BASE_URL}${targetPath}`;

    try {
        const response = await axios({
            method: req.method,
            url: targetUrl,
            headers: req.headers, // Pass through relevant headers
            data: req.body, // Pass through request body for POST/PUT
            params: req.query // Pass through query parameters
        });
        res.status(response.status).json(response.data);
    } catch (error) {
        console.error(`Error proxying API request to ${targetUrl}:`, error.message);
        res.status(error.response?.status || 500).json({ error: 'Failed to proxy request.' });
    }
});


app.get('/', (req, res) => {
    res.send('Basic API Proxy is running. Try /api/posts or /api/v1/users/1');
});

app.listen(port, () => {
    console.log(`API Proxy running on http://localhost:${port}`);
    console.log(`Proxying requests to ${TARGET_API_BASE_URL}`);
});