PAM code cleanup & refactor

Divided functionality into classes, fixed comments +
various other cleanup. BackenAuth no longer increments
sequence on sending password. SQLite busy timeout shortened
to 1 second.

server/modules/authenticator/PAM/PAMAuth/pam_instance.hh

@@ -0,0 +1,41 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+#include "pam_auth.hh"
+
+#include <string>
+#include <maxscale/service.h>
+#include <maxscale/sqlite3.h>
+
+/** The instance class for the client side PAM authenticator, created in pam_auth_init() */
+class PamInstance
+{
+    PamInstance(const PamInstance& orig);
+    PamInstance& operator=(const PamInstance&);
+public:
+    static PamInstance* create(char **options);
+    ~PamInstance();
+    int load_users(SERVICE* service);
+
+    const std::string m_dbname; /**< Name of the in-memory database */
+    const std::string m_tablename; /**< The table where users are stored */
+private:
+    PamInstance(sqlite3* dbhandle, const std::string& m_dbname, const std::string& tablename);
+    void add_pam_user(const char *user, const char *host, const char *db, bool anydb,
+                      const char *pam_service);
+    void delete_old_users();
+
+    sqlite3 * const m_dbhandle; /**< SQLite3 database handle */
+};
+
+