authfs: Add FFI to libcrypto

The FFI is currently used for accessing SHA256 related functions, as
well as SHA256_CTX struct. The whole header is included for bindgen
since we wouldn't want to inline the internal struct definition of
SHA256_CTX.

Bug: 171310075
Test: atest authfs_host_test_src_lib

Change-Id: I0bdec7956d4d0ee407122395fe2b48a437214f3f
diff --git a/authfs/src/crypto.hpp b/authfs/src/crypto.hpp
new file mode 100644
index 0000000..58b0bd3
--- /dev/null
+++ b/authfs/src/crypto.hpp
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef AUTHFS_OPENSSL_WRAPPER_H
+#define AUTHFS_OPENSSL_WRAPPER_H
+
+#include <openssl/sha.h>
+
+#endif  // AUTHFS_OPENSSL_WRAPPER_H