credential/wincred: erase matching creds only

The credential erase request typically includes protocol, host, username
and password.

credential-wincred erases stored credentials that match protocol,
host and username, regardless of password.

This is confusing in the case the stored password differs from that
in the request. This case can occur when multiple credential helpers are
configured.

Only erase credential if stored password matches request (or request
omits password).

This fixes test "helper (wincred) does not erase a password distinct
from input" when t0303 is run with GIT_TEST_CREDENTIAL_HELPER set to
"wincred". This test was added in aeb21ce (credential: avoid
erasing distinct password, 2023-06-13).

Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/credential/wincred/git-credential-wincred.c

@@ -109,7 +109,18 @@ static int match_part_last(LPCWSTR *ptarget, LPCWSTR want, LPCWSTR delim)
 	return match_part_with_last(ptarget, want, delim, 1);
 }
 
-static int match_cred(const CREDENTIALW *cred)
+static int match_cred_password(const CREDENTIALW *cred) {
+	int ret;
+	WCHAR *cred_password = xmalloc(cred->CredentialBlobSize);
+	wcsncpy_s(cred_password, cred->CredentialBlobSize,
+		(LPCWSTR)cred->CredentialBlob,
+		cred->CredentialBlobSize / sizeof(WCHAR));
+	ret = !wcscmp(cred_password, password);
+	free(cred_password);
+	return ret;
+}
+
+static int match_cred(const CREDENTIALW *cred, int match_password)
 {
 	LPCWSTR target = cred->TargetName;
 	if (wusername && wcscmp(wusername, cred->UserName ? cred->UserName : L""))
@@ -119,7 +130,8 @@ static int match_cred(const CREDENTIALW *cred)
 		match_part(&target, protocol, L"://") &&
 		match_part_last(&target, wusername, L"@") &&
 		match_part(&target, host, L"/") &&
-		match_part(&target, path, L"");
+		match_part(&target, path, L"") &&
+		(!match_password || match_cred_password(cred));
 }
 
 static void get_credential(void)
@@ -134,7 +146,7 @@ static void get_credential(void)
 
 	/* search for the first credential that matches username */
 	for (i = 0; i < num_creds; ++i)
-		if (match_cred(creds[i])) {
+		if (match_cred(creds[i], 0)) {
 			write_item("username", creds[i]->UserName,
 				creds[i]->UserName ? wcslen(creds[i]->UserName) : 0);
 			write_item("password",
@@ -196,7 +208,7 @@ static void erase_credential(void)
 		return;
 
 	for (i = 0; i < num_creds; ++i) {
-		if (match_cred(creds[i]))
+		if (match_cred(creds[i], password != NULL))
 			CredDeleteW(creds[i]->TargetName, creds[i]->Type, 0);
 	}