What are CORS headers and how do I use them?

What are CORS headers and how do I use them?

CORS stands for Cross-Origin Resource Sharing. It's a security feature that allows or restricts resources requested from another domain. You use CORS headers to specify which domains are permitted to access your resources.

Can you give me an example of how to set CORS headers in an Express.js application?

Sure! In an Express.js app, you can use the cors middleware. First, install it using npm install cors, then use it like this:

const cors = require('cors');
app.use(cors());

This will allow all domains to access your resources. You can also configure it to allow specific domains.

What if I want to restrict access to only certain domains?

You can specify the allowed origins in the cors middleware like this:

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

This will only allow requests from https://example.com.

Are there any security risks I should be aware of?

Yes, allowing all origins can expose your API to security risks. It's best to restrict access to trusted domains and validate incoming requests.