If an expression in "Require expr" returns denied and

references %{REMOTE_USER}, trigger authentication and retry.
Log error if 'Require expr' fails.

PR: 52892

Backport of r1351071, r1351072 and r1351074 from trunk.

Submitted by: sf
Reviewed by: rjung, trawick
Backported by: rjung


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1364266 13f79535-47bb-0310-9956-ffa450edef68