initial commit: WIP debugging PAM module

pam-module/include/rust_backend_ffi.h

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2026 Suyono
+// 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
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Initialize logging
+void rust_init_logging(const char* log_path);
+
+// Authenticate user (stub)
+int rust_auth_user(const char* user, const char* password);
+
+// Log event (file sink)
+void rust_log_event(const char* event);
+
+#ifdef __cplusplus
+}
+#endif