I'm using a feed reader (ViennaRSS) that requests feeds without sending authentication, and expects a 401 challenge before it will prompt for a username and password. Currently, I get a 302 redirection to the login page instead, which doesn't make sense for a non-interactive client.

In Confluence Cloud, ?os_authType=basic used to cause Confluence to reject unauthenticated requests with a 401 (and WWW-authenticate: basic), which would cause clients to prompt for basic auth credentials. This is currently ignored, and instead a 302 redirection to the login page is served.