The functionality for helpers is already there; we just need
to give the users a way to turn it on.
The new functionality is enabled whenever a caller of the
credentials API passes a NULL method list. This will enable
it for all current callers (i.e., the http code).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>