Adapt portable to legacy buffer API removal
diff --git a/auth.c b/auth.c
index 2dddcf1..f4d2d33 100644
--- a/auth.c
+++ b/auth.c
@@ -79,7 +79,7 @@
 /* import */
 extern ServerOptions options;
 extern int use_privsep;
-extern Buffer loginmsg;
+extern struct sshbuf *loginmsg;
 extern struct passwd *privsep_pw;
 extern struct sshauthopt *auth_opts;