docs: Mark 'client use spnego principal' as deprecated and also a bad idea.

Bug 10888 - smbclient doesn't ignore "not_defined_in_RFC4178@please_ignore"

https://bugzilla.samba.org/show_bug.cgi?id=10888

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Stefan (metze) Metzmacher <metze@samba.org>

docs-xml/smbdotconf/security/clientusepsnegoprincipal.xml

@@ -14,6 +14,10 @@
     servers known only by IP address.  Kerberos relies on names, so
     ordinarily cannot function in this situation. </para>
 
+    <para>This is a VERY BAD IDEA for security reasons, and so this
+    parameter SHOULD NOT BE USED. It will be removed in a future
+    version of Samba.</para>
+
     <para>If disabled, Samba will use the name used to look up the
     server when asking the KDC for a ticket.  This avoids situations
     where a server may impersonate another, soliciting authentication
@@ -23,6 +27,9 @@
     <para>Note that Windows XP SP2 and later versions already follow
     this behaviour, and Windows Vista and later servers no longer
     supply this 'rfc4178 hint' principal on the server side.</para>
+
+    <para>This parameter is deprecated in Samba 4.2.1 and will be removed
+    (along with the functionality) in a later release of Samba.</para>
 </description>
 <value type="default">no</value>
 </samba:parameter>

lib/param/param_table.c

@@ -765,7 +765,7 @@ struct parm_struct parm_table[] = {
 		.offset		= GLOBAL_VAR(client_use_spnego_principal),
 		.special	= NULL,
 		.enum_list	= NULL,
-		.flags		= FLAG_ADVANCED,
+		.flags		= FLAG_ADVANCED | FLAG_DEPRECATED,
 	},
 	{
 		.label		= "username",