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_client_session.hh

@@ -0,0 +1,46 @@
+#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 <stdint.h>
+#include <string>
+#include <vector>
+#include <maxscale/sqlite3.h>
+#include "pam_instance.hh"
+#include "../pam_auth_common.hh"
+
+/** Client authenticator PAM-specific session data */
+class PamClientSession
+{
+    PamClientSession(const PamClientSession& orig);
+    PamClientSession& operator=(const PamClientSession&);
+public:
+    typedef std::vector<std::string> StringVector;
+    static PamClientSession* create(const PamInstance& inst);
+    ~PamClientSession();
+    int authenticate(DCB* client);
+    int extract(DCB *dcb, GWBUF *read_buffer);
+private:
+    PamClientSession(sqlite3* dbhandle, const PamInstance& instance);
+    void get_pam_user_services(const DCB* dcb, const MYSQL_session* session,
+                               StringVector* services_out);
+    maxscale::Buffer create_auth_change_packet() const;
+
+    pam_auth_state m_state; /**< Authentication state*/
+    uint8_t m_sequence; /**< The next packet seqence number */
+    sqlite3* const m_dbhandle; /**< SQLite3 database handle */
+    const PamInstance& m_instance; /**< Authenticator instance */
+};
+
+