t5551: test http interaction with credential helpers

We test authentication with http, and we independently test that
credential helpers work, but we don't have any tests that cover the
two features working together. Let's add two:

  1. Make sure that a successful request asks the helper to save the
     credential. This works as expected.

  2. Make sure that a failed request asks the helper to forget the
     credential. This is marked as expect_failure, as it was recently
     regressed by 1b0d9545bb (remote-curl: fall back to basic auth if
     Negotiate fails, 2021-03-22). The symptom here is that the second
     request should prompt the user, but doesn't.

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

t/t5551-http-fetch-smart.sh

@@ -517,4 +517,45 @@ test_expect_success 'server-side error detected' '
 	test_i18ngrep "server-side error" actual
 '
 
+test_expect_success 'http auth remembers successful credentials' '
+	rm -f .git-credentials &&
+	test_config credential.helper store &&
+
+	# the first request prompts the user...
+	set_askpass user@host pass@host &&
+	git ls-remote "$HTTPD_URL/auth/smart/repo.git" >/dev/null &&
+	expect_askpass both user@host &&
+
+	# ...and the second one uses the stored value rather than
+	# prompting the user.
+	set_askpass bogus-user bogus-pass &&
+	git ls-remote "$HTTPD_URL/auth/smart/repo.git" >/dev/null &&
+	expect_askpass none
+'
+
+test_expect_failure 'http auth forgets bogus credentials' '
+	# seed credential store with bogus values. In real life,
+	# this would probably come from a password which worked
+	# for a previous request.
+	rm -f .git-credentials &&
+	test_config credential.helper store &&
+	{
+		echo "url=$HTTPD_URL" &&
+		echo "username=bogus" &&
+		echo "password=bogus"
+	} | git credential approve &&
+
+	# we expect this to use the bogus values and fail, never even
+	# prompting the user...
+	set_askpass user@host pass@host &&
+	test_must_fail git ls-remote "$HTTPD_URL/auth/smart/repo.git" >/dev/null &&
+	expect_askpass none &&
+
+	# ...but now we should have forgotten the bad value, causing
+	# us to prompt the user again.
+	set_askpass user@host pass@host &&
+	git ls-remote "$HTTPD_URL/auth/smart/repo.git" >/dev/null &&
+	expect_askpass both user@host
+'
+
 test_done