How to match a Drupal path in Apache config
The directive I was trying to insert was Require all granted.  I managed to achieve the same effect by proxy-passing requests for /foo/bar to another virtual host running on the same machine, but unreachable from outside.  That 2nd virtual host did not require auth, which achieved the same effect as Require all granted.

ProxyPass /foo/bar http://example.local/foo/bar
ProxyPassReverse /foo/bar http://example.local/foo/bar