On FreeBSD 9, the Port security/openvpn-auth-ldap is flagged as BROKEN because of the following error in the configure build step.

configure: WARNING: Check library not found. Unit tests will not be built or run.
checking for openvpn-plugin.h... no
configure: error: Could not locate a working openvpn source tree.
See `config.log' for more details.
===> Script "configure" failed unexpectedly.
Please report the problem to snb@FreeBSD.org [maintainer] and attach the
"/usr/ports/security/openvpn-auth-ldap/work/auth-ldap-2.0.3/config.log"
including the output of the failure of your make command. Also, it might be
a good idea to provide an overview of all packages installed on your system
(e.g. a /usr/sbin/pkg_info -Ea).
*** Error code 1

Looking at the config.log, we have:

configure:5511: checking for openvpn-plugin.h
configure:5544: cc -o conftest -O2 -pipe -DLDAP_DEPRECATED -fno-strict-aliasing -I/usr/ports/security/openvpn/work/openvpn-2.3.0 -export-dynamic conftest.c >&5
conftest.c:15:34: error: openvpn-plugin.h: No such file or directory

Other error that might happen:

checking how to run the Objective C preprocessor... /lib/cpp
configure: error: Objective C preprocessor "/lib/cpp" fails sanity check

To fix this, a patch can be applied:

cd /usr/ports/security/openvpn-auth-ldap
wget https://mwclabs.net/pub/openvpn-auth-ldap.patch
patch -p0 < openvpn-auth-ldap.patch
make && make install