The approach for allowing authorization by user or IP introduced in r956387,

The approach for allowing authorization by user or IP introduced in r956387,
etc. causes problems because the authentication module calls
note_*_auth_failure if authentication fails. This is inappropriate if access is
later allowed because of the IP.

So, instead of calling the auth_checker hook even if authentication failed, we
introduce a new access_checker_ex hook that runs between the access_checker and
the check_user_id hooks. If an access_checker_ex functions returns OK, the
request will be allowed without authentication.

To make use of this, change mod_authz_core to walk the require blocks in the
access_checker_ex phase and deny/allow the request if the authz result does not
depend on an authenticated user. To distinguish a real AUTHZ_DENIED from an
authz provider from an authz provider needing an authenticated user, the latter
must return the new AUTHZ_DENIED_NO_USER code.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@964156 13f79535-47bb-0310-9956-ffa450edef68