This allows you to use the samba style @netgroup names in hosts allow
and hosts deny.

This patch still needs autoconf support for portability.

To use this patch, run these commands for a successful build:

    patch -p1 <patches/netgroup-auth.diff
    ./configure                           (optional if already run)
    make

based-on: d73762eea3f15f2c56bb3fa9394ad1883c25c949
diff --git a/access.c b/access.c
--- a/access.c
+++ b/access.c
@@ -19,6 +19,7 @@
  */
 
 #include "rsync.h"
+#include <netdb.h>
 
 static int allow_forward_dns;
 
@@ -33,6 +34,9 @@ static int match_hostname(const char **host_ptr, const char *addr, const char *t
 	if (!host || !*host)
 		return 0;
 
+	if (*tok == '@' && tok[1])
+		return innetgr(tok + 1, host, NULL, NULL);
+
 	/* First check if the reverse-DNS-determined hostname matches. */
 	if (iwildmatch(tok, host))
 		return 1;