CORS Configuration in Node.js

const cors = require('cors');

// Allow all origins (development)
app.use(cors());

// Specific origin
app.use(cors({
  origin: 'https://example.com'
}));

// Multiple origins
const corsOptions = {
  origin: function (origin, callback) {
    const allowedOrigins = ['https://example.com', 'https://app.example.com'];
    if (allowedOrigins.indexOf(origin) !== -1 || !origin) {
      callback(null, true);
    } else {
      callback(new Error('Not allowed by CORS'));
    }
  },
  credentials: true // Allow cookies
};

app.use(cors(corsOptions));