acert: Implement a plugin finding, validating and evaluating attribute certs

This validator checks for any attribute certificate it can find for validated
end entity certificates and tries to extract group membership information
used for connection authorization rules.

src/libstrongswan/Makefile.am

@@ -307,6 +307,13 @@ if MONOLITHIC
 endif
 endif
 
+if USE_ACERT
+  SUBDIRS += plugins/acert
+if MONOLITHIC
+  libstrongswan_la_LIBADD += plugins/acert/libstrongswan-acert.la
+endif
+endif
+
 if USE_PUBKEY
   SUBDIRS += plugins/pubkey
 if MONOLITHIC