Hands-On Swift 5 Microservices Development

CORS

This middleware is answering the OPTIONS request by merely returning it positively without doing anything else. Browsers send an OPTIONS request to hosts that are different from the originating file. So, for example, if you run your frontend under https://www.domain.com and your API from https://api.domain.com, then the browsers will send out an OPTIONS request because www.domain.com is not equal to api.domain.com. There is nothing wrong with this, and this handy middleware takes care of it for us.

You can also forward requests going into www.domain.com/api to api.domain.com and, by doing so, prevent the requests from leaving the original domain, so browsers won't send this request either. It depends on the frontend design, though, and ...