Wire up fizz::DefaultFactory to compile time setting

Summary:
`fizz::DefaultFactory` is intended to be a type alias to a compile time
configured instance of the Factory implementation. Several internal Fizz
components (e.g. such as HPKE) may need to create an instance of a Hasher
or an instance of a KeyExchange, so they use fizz::DefaultFactory().

Reviewed By: zalecodez

Differential Revision: D61241067

fbshipit-source-id: 382b39f5be465d2ef234e7d0432d0a53728cc802

fizz/fizz-config.h.in

@@ -14,3 +14,6 @@
 #cmakedefine01 FIZZ_HAVE_LIBAEGIS
 #cmakedefine01 FIZZ_CERTIFICATE_USE_OPENSSL_CERT
 #cmakedefine01 FIZZ_HAVE_OQS
+
+#define FIZZ_DEFAULT_FACTORY_HEADER <fizz/protocol/MultiBackendFactory.h>
+#define FIZZ_DEFAULT_FACTORY ::fizz::MultiBackendFactory

fizz/protocol/BUCK

@@ -126,7 +126,8 @@ cpp_library(
         "DefaultFactory.h",
     ],
     exported_deps = [
-        ":multi_backend_factory",
+        ":multi_backend_factory",  #@manual
+        "//fizz:config",
     ],
 )
 

fizz/protocol/DefaultFactory.h

@@ -8,17 +8,16 @@
 
 #pragma once
 
-#include <fizz/protocol/MultiBackendFactory.h>
+#include <fizz/fizz-config.h>
 
-namespace fizz {
-
-// TODO: This needs to be wired up from fizz-config.h
+#include FIZZ_DEFAULT_FACTORY_HEADER
 
+namespace fizz {
 /**
  * DefaultFactory is a type alias that points to a concrete, non-abstract
  * Factory instance that can be used by various internal components of Fizz
  * to get the "default compile time configured" Factory.
  */
-using DefaultFactory = ::fizz::MultiBackendFactory;
+using DefaultFactory = FIZZ_DEFAULT_FACTORY;
 
 } // namespace fizz