credential/wincred: store oauth_refresh_token

a5c7656 (credential: new attribute oauth_refresh_token) introduced
a new confidential credential attribute and added support to
credential-cache. Later 0ce02e2 (credential/libsecret: store new
attributes, 2023-06-16) added support in credential-libsecret.

To add support in credential-wincred, we encode the new attribute in the
CredentialBlob, separated by newline:

    hunter2
    oauth_refresh_token=xyzzy

This is extensible and backwards compatible. The credential protocol
already assumes that attribute values do not contain newlines.

This fixes test "helper (wincred) gets oauth_refresh_token" when
t0303-credential-external.sh is run with
GIT_TEST_CREDENTIAL_HELPER=wincred. This test was added in a5c7656
(credential: new attribute oauth_refresh_token, 2023-04-21).

Alternatives considered: store oauth_refresh_token in a wincred
attribute. This would be insecure because wincred assumes attribute
values to be non-confidential.

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

Author: hickford

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

@@ -35,7 +35,7 @@ static void *xmalloc(size_t size)
 }
 
 static WCHAR *wusername, *password, *protocol, *host, *path, target[1024],
-	*password_expiry_utc;
+	*password_expiry_utc, *oauth_refresh_token;
 
 static void write_item(const char *what, LPCWSTR wbuf, int wlen)
 {
@@ -128,6 +128,11 @@ static void get_credential(void)
 	DWORD num_creds;
 	int i;
 	CREDENTIAL_ATTRIBUTEW *attr;
+	WCHAR *secret;
+	WCHAR *line;
+	WCHAR *remaining_lines;
+	WCHAR *part;
+	WCHAR *remaining_parts;
 
 	if (!CredEnumerateW(L"git:*", 0, &num_creds, &creds))
 		return;
@@ -137,9 +142,24 @@ static void get_credential(void)
 		if (match_cred(creds[i])) {
 			write_item("username", creds[i]->UserName,
 				creds[i]->UserName ? wcslen(creds[i]->UserName) : 0);
-			write_item("password",
-				(LPCWSTR)creds[i]->CredentialBlob,
-				creds[i]->CredentialBlobSize / sizeof(WCHAR));
+			if (creds[i]->CredentialBlobSize > 0) {
+				secret = xmalloc(creds[i]->CredentialBlobSize);
+				wcsncpy_s(secret, creds[i]->CredentialBlobSize, (LPCWSTR)creds[i]->CredentialBlob, creds[i]->CredentialBlobSize / sizeof(WCHAR));
+				line = wcstok_s(secret, L"\r\n", &remaining_lines);
+				write_item("password", line, line ? wcslen(line) : 0);
+				while(line != NULL) {
+					part = wcstok_s(line, L"=", &remaining_parts);
+					if (!wcscmp(part, L"oauth_refresh_token")) {
+						write_item("oauth_refresh_token", remaining_parts, remaining_parts ? wcslen(remaining_parts) : 0);
+					}
+					line = wcstok_s(NULL, L"\r\n", &remaining_lines);
+				}
+				free(secret);
+			} else {
+				write_item("password",
+						(LPCWSTR)creds[i]->CredentialBlob,
+						creds[i]->CredentialBlobSize / sizeof(WCHAR));
+			}
 			for (int j = 0; j < creds[i]->AttributeCount; j++) {
 				attr = creds[i]->Attributes + j;
 				if (!wcscmp(attr->Keyword, L"git_password_expiry_utc")) {
@@ -158,16 +178,26 @@ static void store_credential(void)
 {
 	CREDENTIALW cred;
 	CREDENTIAL_ATTRIBUTEW expiry_attr;
+	WCHAR *secret;
+	int wlen;
 
 	if (!wusername || !password)
 		return;
 
+	if (oauth_refresh_token) {
+		wlen = _scwprintf(L"%s\r\noauth_refresh_token=%s", password, oauth_refresh_token);
+		secret = xmalloc(sizeof(WCHAR) * wlen);
+		_snwprintf_s(secret, sizeof(WCHAR) * wlen, wlen, L"%s\r\noauth_refresh_token=%s", password, oauth_refresh_token);
+	} else {
+		secret = _wcsdup(password);
+	}
+
 	cred.Flags = 0;
 	cred.Type = CRED_TYPE_GENERIC;
 	cred.TargetName = target;
 	cred.Comment = L"saved by git-credential-wincred";
-	cred.CredentialBlobSize = (wcslen(password)) * sizeof(WCHAR);
-	cred.CredentialBlob = (LPVOID)password;
+	cred.CredentialBlobSize = wcslen(secret) * sizeof(WCHAR);
+	cred.CredentialBlob = (LPVOID)_wcsdup(secret);
 	cred.Persist = CRED_PERSIST_LOCAL_MACHINE;
 	cred.AttributeCount = 0;
 	cred.Attributes = NULL;
@@ -182,6 +212,8 @@ static void store_credential(void)
 	cred.TargetAlias = NULL;
 	cred.UserName = wusername;
 
+	free(secret);
+
 	if (!CredWriteW(&cred, 0))
 		die("CredWrite failed");
 }
@@ -253,6 +285,8 @@ static void read_credential(void)
 			password = utf8_to_utf16_dup(v);
 		else if (!strcmp(buf, "password_expiry_utc"))
 			password_expiry_utc = utf8_to_utf16_dup(v);
+		else if (!strcmp(buf, "oauth_refresh_token"))
+			oauth_refresh_token = utf8_to_utf16_dup(v);
 		/*
 		 * Ignore other lines; we don't know what they mean, but
 		 * this future-proofs us when later versions of git do