Add pam service module for user-linked API keys (#409)

This commit adds a dedicated PAM service module for evaluating
user-linked API keys per discussion in NEP-053. Each user may
have one or more keys associated with themselves. Each key is
hashed using pbkdf2-sha512 with a minimum of 300000 iterations.

The module only provides pam_sm_authenticate, other pam
service module functions are stubbed-out.

debian/truenas-samba.install

@@ -76,6 +76,7 @@ usr/share/ctdb/events/legacy/*.script
 lib/*/libnss_winbind.so.2
 lib/*/libnss_wins.so.2
 lib/*/security/pam_winbind.so
+lib/*/security/pam_tdb.so
 usr/share/pam-configs/winbind
 usr/lib/*/samba/*
 usr/include/samba-4.0/libsmbclient.h

lib/tdb/wscript

@@ -127,6 +127,7 @@ def build(bld):
         bld.SAMBA_LIBRARY('tdb',
                           COMMON_SRC,
                           deps=tdb_deps,
+                          provide_builtin_linking=True,
                           includes='include',
                           abi_directory='ABI',
                           abi_match='tdb_*',