ui/dbus: on win32, allow ANONYMOUS with p2p

GLib doesn't implement EXTERNAL on win32 at the moment, and disables
ANONYMOUS by default. zbus dropped support for COOKIE_SHA1 in 5.0,
making it no longer possible to connect to qemu -display dbus.

Since p2p connections are gated by existing QMP (or a D-Bus connection),
qemu -display dbus p2p can accept authentication with ANONYMOUS.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

audio/dbusaudio.c

@@ -524,11 +524,17 @@ dbus_audio_register_listener(AudioState *s,
             );
     }
 
+    GDBusConnectionFlags flags =
+        G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER;
+#ifdef WIN32
+    flags |= G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_ALLOW_ANONYMOUS;
+#endif
+
     listener_conn =
         g_dbus_connection_new_sync(
             G_IO_STREAM(socket_conn),
             guid,
-            G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER,
+            flags,
             NULL, NULL, &err);
     if (err) {
         error_report("Failed to setup peer connection: %s", err->message);

ui/dbus-console.c

@@ -305,10 +305,16 @@ dbus_console_register_listener(DBusDisplayConsole *ddc,
 #endif
     );
 
+    GDBusConnectionFlags flags =
+        G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER;
+#ifdef WIN32
+    flags |= G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_ALLOW_ANONYMOUS;
+#endif
+
     listener_conn = g_dbus_connection_new_sync(
         G_IO_STREAM(socket_conn),
         guid,
-        G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER,
+        flags,
         NULL, NULL, &err);
     if (err) {
         error_report("Failed to setup peer connection: %s", err->message);

ui/dbus.c

@@ -317,11 +317,17 @@ dbus_display_add_client(int csock, Error **errp)
     conn = g_socket_connection_factory_create_connection(socket);
 
     dbus_display->add_client_cancellable = g_cancellable_new();
+    GDBusConnectionFlags flags =
+        G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER |
+        G_DBUS_CONNECTION_FLAGS_DELAY_MESSAGE_PROCESSING;
+
+#ifdef WIN32
+    flags |= G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_ALLOW_ANONYMOUS;
+#endif
 
     g_dbus_connection_new(G_IO_STREAM(conn),
                           guid,
-                          G_DBUS_CONNECTION_FLAGS_AUTHENTICATION_SERVER |
-                          G_DBUS_CONNECTION_FLAGS_DELAY_MESSAGE_PROCESSING,
+                          flags,
                           NULL,
                           dbus_display->add_client_cancellable,
                           dbus_display_add_client_ready,