[http] Allow for domain names within NTLM user names

Allow a NetBIOS domain name to be specified within a URL using a
syntax such as:

  http://domain%5Cusername:password@server/path

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/netbios.c

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2018 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * NetBIOS user names
+ *
+ */
+
+#include <stddef.h>
+#include <string.h>
+#include <ipxe/netbios.h>
+
+/**
+ * Split NetBIOS [domain\]username into separate domain and username fields
+ *
+ * @v username		NetBIOS [domain\]username string
+ * @ret domain		Domain portion of string, or NULL if no domain present
+ *
+ * This function modifies the original string by removing the
+ * separator.  The caller may restore the string using
+ * netbios_domain_undo().
+ */
+const char * netbios_domain ( char **username ) {
+	char *domain_username = *username;
+	char *sep;
+
+	/* Find separator, if present */
+	sep = strchr ( domain_username, '\\' );
+	if ( ! sep )
+		return NULL;
+
+	/* Overwrite separator with NUL terminator and update username string */
+	*sep = '\0';
+	*username = ( sep + 1 );
+
+	return domain_username;
+}