Zero out auth structs before transfer

lib/transfer.c

@@ -1433,6 +1433,10 @@ CURLcode Curl_pretransfer(struct SessionHandle *data)
 
   data->state.ssl_connect_retry = FALSE;
 
+  /* zero out auth state */
+  memset(&data->state.authhost, 0, sizeof(struct auth));
+  memset(&data->state.authproxy, 0, sizeof(struct auth));
+
   data->state.authproblem = FALSE;
   data->state.authhost.want = data->set.httpauth;
   data->state.authproxy.want = data->set.proxyauth;