Not possible to modify content-type?

I'm using Buddy with Basic Auth and the `api-defaults` Ring middleware. The Unauthorized response gets a `Content-Type` of `octet-stream`. In a (Safari) browser, this results in an empty file being downloaded on Esc from the Basic Auth dialog.

I'm looking for a way to set `Content-Type` to say `text/plain`, but without having to re-create the same response as Buddy Auth. The only solution now seems to be to create a full response myself in the `:on-error` function.