credential: let helpers tell us to quit

When we are trying to fill a credential, we loop over the
set of defined credential-helpers, then fall back to running
askpass, and then finally prompt on the terminal. Helpers
which cannot find a credential are free to tell us nothing,
but they cannot currently ask us to stop prompting.

This patch lets them provide a "quit" attribute, which asks
us to stop the process entirely (avoiding running more
helpers, as well as the askpass/terminal prompt).

This has a few possible uses:

  1. A helper which prompts the user itself (e.g., in a
     dialog) can provide a "cancel" button to the user to
     stop further prompts.

  2. Some helpers may know that prompting cannot possibly
     work. For example, if their role is to broker a ticket
     from an external auth system and that auth system
     cannot be contacted, there is no point in continuing
     (we need a ticket to authenticate, and the user cannot
     provide one by typing it in).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/credential.c b/credential.c
index 4d79d320f8..0f974f1987 100644
--- a/credential.c
+++ b/credential.c
@@ -173,6 +173,8 @@ int credential_read(struct credential *c, FILE *fp)
 			c->path = xstrdup(value);
 		} else if (!strcmp(key, "url")) {
 			credential_from_url(c, value);
+		} else if (!strcmp(key, "quit")) {
+			c->quit = !!git_config_bool("quit", value);
 		}
 		/*
 		 * Ignore other lines; we don't know what they mean, but
@@ -275,6 +277,9 @@ void credential_fill(struct credential *c)
 		credential_do(c, c->helpers.items[i].string, "get");
 		if (c->username && c->password)
 			return;
+		if (c->quit)
+			die("credential helper '%s' told us to quit",
+			    c->helpers.items[i].string);
 	}
 
 	credential_getpass(c);