Add skeleton of authentication

Main logic of it is not implemented yet.

src/pam_maintainance.cpp

@@ -0,0 +1,100 @@
+/**
+ * @file pam_maintainance.cpp
+ * @author Ali Hatami Tajik (info@alihatamitajik.ir)
+ * @brief PAM Module for Sono Maintainance
+ * @version 0.1
+ * @date 2023-05-06
+ * 
+ * @copyright Copyright (c) 2023
+ * 
+ */
+
+#define PAM_SM_AUTH
+#include <security/pam_modules.h>
+#include <security/_pam_macros.h>
+#include <security/pam_ext.h>
+
+#include <syslog.h>
+
+#include "rules.h"
+
+bool
+is_ssh(pam_handle_t *pamh)
+{
+    char *tty;
+    int result = pam_get_item(pamh, PAM_TTY, (const void **)&tty);
+    return result != PAM_SUCCESS || 
+           (tty != NULL && strncmp(tty, "ssh", 3) == 0);
+}
+
+bool
+is_user_valid(pam_handle_t *pamh, const char **user)
+{
+    int result = pam_get_user(pamh, user, NULL);
+    return result == PAM_SUCCESS &&
+           *user != NULL &&
+           **user != '\0';
+}
+
+bool 
+validate_rsa()
+{
+    return false;
+}
+
+bool
+authenticate(const char *user)
+{
+    for (size_t i = 0; i < LEN(rules); i++)
+    {
+        if (strcmp(rules[i].username, user) == 0) {
+            if (rules[i].auth == FREE)
+                return true;
+            else if (rules[i].auth == RSA)
+                return validate_rsa();
+            else {
+                return false;
+            }
+        }
+    }
+
+    return false;
+}
+
+PAM_EXTERN int
+pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+    const char *user;
+
+    pam_syslog(pamh, LOG_USER | LOG_DEBUG,
+               "PAM Maintainance: Auth Activated.\n");
+
+    if (is_ssh(pamh)) {
+        pam_syslog(pamh, LOG_USER | LOG_DEBUG, 
+                   "PAM Maintainance: FAILED, SSH call.\n");
+        return PAM_AUTH_ERR;
+    }
+
+    if (!is_user_valid(pamh, &user)) {
+        pam_syslog(pamh, LOG_USER | LOG_DEBUG,
+                   "PAM Maintainance: FAILED, Unable to get user.\n");
+        return PAM_AUTH_ERR;
+    }
+
+    if (authenticate(user)) {
+        pam_syslog(pamh, LOG_USER | LOG_DEBUG, 
+                   "PAM Maintainance: Access Granted.\n");
+        return PAM_SUCCESS;
+    } else {
+        pam_syslog(pamh, LOG_USER | LOG_USER,
+                   "PAM Maintainance: FAILED, Matched no rule.\n");
+        return PAM_AUTH_ERR;
+    }
+}
+
+
+PAM_EXTERN int
+pam_sm_setcred(pam_handle_t *pamh, int flags, int argc, const char **argv)
+{
+    return PAM_SUCCESS;
+}

src/rules.h

@@ -0,0 +1,18 @@
+
+#define LEN(X) (sizeof X / sizeof X[0])
+#define _SIGNATURE_PLAIN "*******"
+#define _PUBLIC_KEY_FILE "*******"
+
+typedef enum authentication {FREE, RSA} auth_t;
+
+typedef struct {
+    const char *username;
+    auth_t auth;
+} rule, *rule_t;
+
+
+static const rule rules[] = 
+{
+    {"doctor", FREE},
+    {"support", RSA}
+};