Add CORS headers in preview mode

[lfkpoa]

Hello,

We use Observable with API calls to a few different servers. The users connect with their own ID to these servers to get the data if they are authorized. But I can't use Observable Framework preview server while developing because of CORS. When I create react apps with create-react-app, their preview server (npm start) adds CORS headers automatically and I can test the app:

access-control-allow-headers: *
access-control-allow-methods: *
access-control-allow-origin: *

So, I'm suggesting to add these CORS headers automatically to the preview server as well or, at least, add a config that enables this feature.

Thank you.