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.h

@@ -0,0 +1,27 @@
+/* -*- 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.
+ */
+
+#ifndef MM_AUTH_H
+#define MM_AUTH_H
+
+#include "mm-auth-provider.h"
+
+/* Get the default provider */
+MMAuthProvider *mm_auth_get_provider (void);
+
+void mm_auth_shutdown (void);
+
+#endif /* MM_AUTH_H */