REP-382 OpenStack Basic Auth filter creation

I wasn't sure either. After some research, I ended up adding the comment below to the FilterDirector's setFilterAction() method:
Informs the Filter Chain whether to continue (PASS), stop and return immediately (RETURN), or continue and then handle the response on the unwind (PROCESS_RESPONSE).

In other words this filter does need access to the response when the filter chain is unwinding. The handleResponse() is what adds the WWW_AUTHENTICATE:Basic header if something down the filter chain sets the Response Status Code to UNAUTHORIZED (401) OR FORBIDDEN (403).