allow the user to configure credential helpers

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>

Documentation/technical/api-credentials.txt

@@ -25,8 +25,9 @@ Data Structures
 	The credential functions take a `string_list` of methods for
 	acquiring credentials. Each string specifies an external
 	helper which will be run, in order, to acquire credentials,
-	until both a username and password have been acquired. A NULL or
-	empty methods list indicates that the internal
+	until both a username and password have been acquired. A NULL
+	parameter means to use the default list (as configured by
+	`credential.helper`); an empty list indicates that the internal
 	`credential_getpass` function should be used.
 
 

config.c

@@ -9,6 +9,7 @@
 #include "exec_cmd.h"
 #include "strbuf.h"
 #include "quote.h"
+#include "credential.h"
 
 #define MAXNAME (256)
 
@@ -791,6 +792,9 @@ int git_default_config(const char *var, const char *value, void *dummy)
 		return 0;
 	}
 
+	if (!prefixcmp(var, "credential."))
+		return git_default_credential_config(var, value);
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }

credential.c

@@ -4,6 +4,8 @@
 #include "string-list.h"
 #include "run-command.h"
 
+static struct string_list default_methods;
+
 static int credential_config_callback(const char *var, const char *value,
 				      void *data)
 {
@@ -173,15 +175,18 @@ void credential_fill(struct credential *c, const struct string_list *methods)
 {
 	struct strbuf err = STRBUF_INIT;
 
+	if (!methods)
+		methods = &default_methods;
+
 	if (!credential_fill_gently(c, methods))
 		return;
 
 	strbuf_addstr(&err, "unable to get credentials");
 	if (c->description)
 		strbuf_addf(&err, "for '%s'", c->description);
-	if (methods && methods->nr == 1)
+	if (methods->nr == 1)
 		strbuf_addf(&err, "; tried '%s'", methods->items[0].string);
-	else if (methods) {
+	else {
 		int i;
 		strbuf_addstr(&err, "; tried:");
 		for (i = 0; i < methods->nr; i++)
@@ -198,7 +203,10 @@ int credential_fill_gently(struct credential *c,
 	if (c->username && c->password)
 		return 0;
 
-	if (!methods || !methods->nr)
+	if (!methods)
+		methods = &default_methods;
+
+	if (!methods->nr)
 		return credential_getpass(c);
 
 	for (i = 0; i < methods->nr; i++) {
@@ -214,7 +222,10 @@ void credential_reject(struct credential *c, const struct string_list *methods)
 {
 	int i;
 
-	if (methods && c->username) {
+	if (!methods)
+		methods = &default_methods;
+
+	if (c->username) {
 		for (i = 0; i < methods->nr; i++) {
 			/* ignore errors, there's nothing we can do */
 			credential_do(c, methods->items[i].string, "--reject");
@@ -226,3 +237,15 @@ void credential_reject(struct credential *c, const struct string_list *methods)
 	free(c->password);
 	c->password = NULL;
 }
+
+int git_default_credential_config(const char *var, const char *value)
+{
+	if (!strcmp(var, "credential.helper")) {
+		if (!value)
+			return config_error_nonbool(var);
+		string_list_append(&default_methods, xstrdup(value));
+		return 0;
+	}
+
+	return 0;
+}

credential.h

@@ -17,4 +17,6 @@ int credential_fill_gently(struct credential *, const struct string_list *method
 void credential_fill(struct credential *, const struct string_list *methods);
 void credential_reject(struct credential *, const struct string_list *methods);
 
+int git_default_credential_config(const char *var, const char *value);
+
 #endif /* CREDENTIAL_H */

t/t5550-http-fetch.sh

@@ -93,6 +93,19 @@ test_expect_success 'http auth can pull user from config' '
 	test_cmp askpass-expect-pass askpass-query
 '
 
+test_expect_success 'http auth respects credential helpers' '
+	cat >credential-helper <<-\EOF &&
+	#!/bin/sh
+	echo username=user@host
+	echo password=user@host
+	EOF
+	chmod +x credential-helper &&
+	git config --global credential.helper "\"$PWD/credential-helper\"" &&
+	>askpass-query &&
+	git clone "$HTTPD_URL/auth/repo.git" clone-auth-helper &&
+	test_cmp askpass-expect-none askpass-query
+'
+
 test_expect_success 'fetch changes via http' '
 	echo content >>file &&
 	git commit -a -m two &&