auth: refactor and simplify authentication related setup

We get rid of the MMAuthRequests; and we leave up to the caller and user of the
MMAuthProvider the handling of request cancellations through the provided
GCancellable.

Also made GIO-async-friendly methods.

src/mm-auth.c

@@ -0,0 +1,53 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details:
+ *
+ * Copyright (C) 2010 - 2012 Red Hat, Inc.
+ * Copyright (C) 2012 Google, Inc.
+ */
+
+#include <string.h>
+
+#include "config.h"
+
+#include "mm-auth.h"
+#include "mm-auth-provider.h"
+
+#ifdef WITH_POLKIT
+#include "mm-auth-provider-polkit.h"
+#endif
+
+static MMAuthProvider *authp = NULL;
+
+MMAuthProvider *
+mm_auth_get_provider (void)
+{
+    if (!authp) {
+#if WITH_POLKIT
+        authp = mm_auth_provider_polkit_new ();
+#else
+        authp = mm_auth_provider_new ();
+#endif
+    }
+
+    g_assert (authp);
+
+    /* We'll keep the refcount of this object controlled, in order to have
+     * clean shutdowns */
+    return g_object_ref (authp);
+}
+
+void
+mm_auth_shutdown (void)
+{
+    /* Clear the last reference of the auth provider if it was ever set */
+    g_clear_object (&authp);
+}