modules: Add stirshaken module

This module uses libstirshaken to implement STIR-Shaken authentication and verification functions (STI-AS/VS).
It allows for easy verification of a SIP call containing PASSporT wrapped into SIP Identity Header using a specific certificate,
or a specific key, or by performing complete check on PASSporT including downloading certificate referenced in it's x5u header,
and optionally checking it against trusted root certificates (X509 cert path check). Certificates may be cached and loaded from disk.

Example usage:

loadmodule "stirshaken"
modparam("stirshaken", "as_default_key", "/path/to/key")

modparam("stirshaken", "vs_verify_x509_cert_path", 1)
modparam("stirshaken", "vs_ca_dir", "/path/to/ca")
modparam("stirshaken", "vs_cache_certificates", 1)
modparam("stirshaken", "vs_cache_dir", "/tmp/cert_cache")
modparam("stirshaken", "vs_cache_expire_s", 90)

request_route {
	(...)
	stirshaken_add_identity("https://sp.com/sp.pem", "B", "+44100", "+44200", "ref");
	(...)

request_route {
	(...)
	stirshaken_check_identity();
	(...)

src/modules/stirshaken/Makefile

@@ -0,0 +1,28 @@
+#
+# stirshaken module makefile
+#
+# WARNING: do not run this directly, it should be run by the main Makefile
+
+include ../../Makefile.defs
+auto_gen=
+NAME=stirshaken.so
+
+ifeq ($(CROSS_COMPILE),)
+	BUILDER = $(shell which pkg-config)
+ifneq ($(BUILDER),)
+	PKGLIBSECSIPID = $(shell $(BUILDER) --exists stirshaken > /dev/null 2>&1 ; echo $$? )
+ifneq ($(PKGLIBSECSIPID),0)
+	BUILDER =
+endif
+endif
+endif
+
+ifeq ($(BUILDER),)
+	DEFS+= -I.
+	LIBS = -L. -lstirshaken
+else
+	DEFS+= $(shell pkg-config --cflags stirshaken)
+	LIBS = $(shell pkg-config --libs stirshaken)
+endif
+
+include ../../Makefile.modules