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/PAMBackendAuth/pam_backend_session.hh

@@ -0,0 +1,39 @@
+/*
+ * 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.
+ */
+
+#ifndef PAMBACKENDSESSION_HH
+#define PAMBACKENDSESSION_HH
+
+#include "pam_backend_auth.hh"
+
+#include <stdint.h>
+#include "../pam_auth_common.hh"
+
+class PamBackendSession
+{
+    PamBackendSession(const PamBackendSession& orig);
+    PamBackendSession& operator=(const PamBackendSession&);
+public:
+    PamBackendSession();
+    int extract(DCB *dcb, GWBUF *buffer);
+    int authenticate(DCB *dcb);
+
+private:
+    bool send_client_password(DCB *dcb);
+
+    pam_auth_state m_state; /**< Authentication state*/
+    uint8_t m_sequence; /**< The next packet seqence number */
+};
+
+#endif /* PAMBACKENDSESSION_HH */
+