pkg install nss-pam-ldapd

Edit /usr/local/etc/nslcd.conf with:

...
uri ldap://ldap.example.com
ldap_version 3
base dc=example,dc=com
scope sub
ssl no

Restart nslcd service:

service nslcd restart

Edit /etc/pam.d/system with the following:

Note: For brevity I'm only showing the pam_ldap and pam_unix lines so you know where they need to be in relation to each other.

...
auth		sufficient	/usr/local/lib/pam_ldap.so	try_first_pass
auth		required	pam_unix.so		no_warn try_first_pass nullok

...
account		required	pam_unix.so
account		required	/usr/local/lib/pam_ldap.so	no_warn	ignore_authinfo_unavail	ignore_unknown_user


...
password	sufficient	/usr/local/lib/pam_ldap.so	no_warn try_first_pass
password	required	pam_unix.so		no_warn try_first_pass

And similar changes to /etc/pam.d/sshd:

...
auth		sufficient	/usr/local/lib/pam_ldap.so	try_first_pass
auth		required	pam_unix.so		no_warn try_first_pass

...
account		required	pam_unix.so
account		required	/usr/local/lib/pam_ldap.so	no_warn	ignore_authinfo_unavail	ignore_unknown_user

...
password	sufficient	/usr/local/lib/pam_ldap.so	no_warn try_first_pass
password	required	pam_unix.so		no_warn try_first_pass

Edit /etc/nsswitch.conf with:

...
group: files ldap
...
passwd: files ldap
...

You can test it by trying to see a user's ID is available:

id exampleuser

You can also try using getent:

getent passwd exampleuser

In both cases you should get some sort of valid output, and in the latter you should see an “x” for the password attribute (meaning it's an external password).

Hurrah! Have fun with your FreeBSD LDAP setup!