Slightly off-topic to the original question … but this seems like an inappropriate server response from an HTTP and API standpoint.
1. The client is sending credentials using HTTP auth (basic or digest). If the credentials are invalid the correct response is a 401 Unauthorized, not a redirect.
2. The URL being redirected to is part of the Futon admin UI. This might be appropriate for an end-user interacting through a browser, but not for an app.
3. The _utils directory isn’t present in all CouchDB installations; e.g. mobile installs, so this redirect might go to a missing page.