### Is there an existing issue for this? - [X] I have searched the existing issues ### Current Behavior The middleware [lists `Origin` as an allowed request header](https://github.com/gorilla/handlers/blob/fc9305756b095d6a0aede51f06fc85933647a25f/cors.go#L31). However, listing `Origin` is never necessary because that header is added to requests by the browser, [never by the client](https://fetch.spec.whatwg.org/#forbidden-request-header). ### Expected Behavior Not listing `Origin` as an allowed request header.