credential: handle `credential.<partial-URL>.<key>` again

In the patches for CVE-2020-11008, the ability to specify credential
settings in the config for partial URLs got lost. For example, it used
to be possible to specify a credential helper for a specific protocol:

	[credential "https://"]
		helper = my-https-helper

Likewise, it used to be possible to configure settings for a specific
host, e.g.:

	[credential "dev.azure.com"]
		useHTTPPath = true

Let's reinstate this behavior.

While at it, increase the test coverage to document and verify the
behavior with a couple other categories of partial URLs.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

credential.c

@@ -35,6 +35,10 @@ int credential_match(const struct credential *want,
 #undef CHECK
 }
 
+
+static int credential_from_potentially_partial_url(struct credential *c,
+						   const char *url);
+
 static int credential_config_callback(const char *var, const char *value,
 				      void *data)
 {
@@ -53,7 +57,13 @@ static int credential_config_callback(const char *var, const char *value,
 		char *url = xmemdupz(key, dot - key);
 		int matched;
 
-		credential_from_url(&want, url);
+		if (credential_from_potentially_partial_url(&want, url) < 0) {
+			warning(_("skipping credential lookup for key: %s"),
+				var);
+			credential_clear(&want);
+			free(url);
+			return 0;
+		}
 		matched = credential_match(&want, c);
 
 		credential_clear(&want);
@@ -430,6 +440,12 @@ static int credential_from_url_1(struct credential *c, const char *url,
 	return 0;
 }
 
+static int credential_from_potentially_partial_url(struct credential *c,
+						   const char *url)
+{
+	return credential_from_url_1(c, url, 1, 0);
+}
+
 int credential_from_url_gently(struct credential *c, const char *url, int quiet)
 {
 	return credential_from_url_1(c, url, 0, quiet);

t/t0300-credentials.sh

@@ -448,4 +448,42 @@ test_expect_success 'credential system refuses to work with missing protocol' '
 	test_i18ncmp expect stderr
 '
 
+test_expect_success 'credential config with partial URLs' '
+	echo "echo password=yep" | write_script git-credential-yep &&
+	test_write_lines url=https://user@example.com/repo.git >stdin &&
+	for partial in \
+		example.com \
+		user@example.com \
+		https:// \
+		https://example.com \
+		https://example.com/ \
+		https://user@example.com \
+		https://user@example.com/ \
+		https://example.com/repo.git \
+		https://user@example.com/repo.git \
+		/repo.git
+	do
+		git -c credential.$partial.helper=yep \
+			credential fill <stdin >stdout &&
+		grep yep stdout ||
+		return 1
+	done &&
+
+	for partial in \
+		dont.use.this \
+		http:// \
+		/repo
+	do
+		git -c credential.$partial.helper=yep \
+			credential fill <stdin >stdout &&
+		! grep yep stdout ||
+		return 1
+	done &&
+
+	git -c credential.$partial.helper=yep \
+		-c credential.with%0anewline.username=uh-oh \
+		credential fill <stdin >stdout 2>stderr &&
+	test_i18ngrep "skipping credential lookup for key" stderr
+'
+
 test_done