Problem with windows credential prompt, CredUnPackAuthenticationBuffer error 50 - c++

Question

I'm trying to display Windows default credential prompt and retrieve username, password and domain as strings.
I'm using this documentation:
CredUIPromptForWindowsCredentialsW
CredUnPackAuthenticationBufferW
When prompt displays, I enter random username and password (like, username: test, password: test123), hit enter and function CredUnPackAuthenticationBuffer() fails with ERROR_NOT_SUPPORTED
Code:
#include <Windows.h>
#include <wincred.h> //Link library Credui.lib for CredUIPromptForWindowsCredentials() to work
#include <iostream>
#include <string>
//Display error in console and close application
void DisplayConsoleError(const WCHAR* errorMessage, const WCHAR* fName);
int wmain(int argc, WCHAR* argv[])
{
CREDUI_INFO cuiInfo;
cuiInfo.cbSize = sizeof(CREDUI_INFO);
cuiInfo.hbmBanner = nullptr;
cuiInfo.hwndParent = nullptr;
cuiInfo.pszCaptionText = L"CaptionText";
cuiInfo.pszMessageText = L"MessageText";
DWORD dwAuthError = 0;
ULONG dwAuthPackage = 0;
LPVOID outCredBuffer = nullptr;
ULONG outCredBufferSize = 0;
BOOL credSaveCheckbox = false;
DWORD dwError = 0;
DWORD lastError = 0;
dwError = CredUIPromptForWindowsCredentials(
&cuiInfo,
dwAuthError,
&dwAuthPackage,
nullptr,
NULL,
&outCredBuffer,
&outCredBufferSize,
&credSaveCheckbox,
CREDUIWIN_CHECKBOX | CREDUIWIN_GENERIC);
if (dwError == ERROR_SUCCESS)
{
DWORD maxUserNameSize = CREDUI_MAX_USERNAME_LENGTH;
DWORD maxDomainNameSize = CREDUI_MAX_DOMAIN_TARGET_LENGTH;
DWORD maxPasswordLength = CREDUI_MAX_PASSWORD_LENGTH;
LPWSTR szUserName = new WCHAR[maxUserNameSize];
LPWSTR szDomain = new WCHAR[maxDomainNameSize];
LPWSTR szPassword = new WCHAR[maxPasswordLength];
DWORD dwCredBufferSize = outCredBufferSize; //ULONG to DWORD
DWORD lastError = 0;
dwError = CredUnPackAuthenticationBuffer(
CRED_PACK_GENERIC_CREDENTIALS,
&outCredBuffer,
dwCredBufferSize,
szUserName,
&maxUserNameSize,
szDomain,
&maxDomainNameSize,
szPassword,
&maxPasswordLength
);
lastError = GetLastError();
//Check for error
if (dwError == FALSE)
{
DisplayConsoleError(L"Blah", L"CredUnPackAuthenticationBuffer", lastError);
}
else
{
std::wcout << L"username " << szUserName << std::endl;
std::wcout << L"domain " << szDomain << std::endl;
std::wcout << L"password " << szPassword << std::endl;
}
}
else
{
lastError = dwError;
}
SecureZeroMemory(outCredBuffer, outCredBufferSize);
CoTaskMemFree(outCredBuffer);
return lastError;
}
Additionaly debugging CredUIPromptForWindowsCredentials() in VS2019 fails (problem with loading symbols?), but compiled .exe works fine. As a workaround im attaching debugger to process.
I'm beginner at winapi, so I would be grateful, if someone would explain why this error appears, what I'm doing wrong and how to fix this code.
EDIT
Moved error check above SecureZeroMemory() and CoTaskMemFree() functions to avoid calling other API functions before checking error message,
but error remained the same.
DisplayConsoleError:
void DisplayConsoleError(const WCHAR* errorMessage, const WCHAR* fName, DWORD lastError)
{
std::cout << std::endl;
std::cout << "Error\t" << std::endl;
std::wcout << L"In function:\t" << fName << std::endl;
std::cout << "Code:\t" << lastError << std::endl;
std::cout << std::endl;
}
EDIT 2 Changes to code considering #RemyLebeau feedback

Answer 1

Look at this function in your code:
CredUnPackAuthenticationBuffer(
CRED_PACK_GENERIC_CREDENTIALS,
&outCredBuffer,
dwCredBufferSize,
szUserName,
&maxUserNameSize,
szDomain,
&maxDomainNameSize,
szPassword,
&maxPasswordLength
);
You need to change &outCredBuffer to outCredBuffer.
#include <Windows.h>
#include <wincred.h> //Link library Credui.lib for CredUIPromptForWindowsCredentials() to work
#include <iostream>
#include <string>
//Display error in console and close application
void DisplayConsoleError(const WCHAR* errorMessage, const WCHAR* fName, DWORD lastError)
{
std::cout << std::endl;
std::cout << "Error\t" << std::endl;
std::wcout << L"In function:\t" << fName << std::endl;
std::cout << "Code:\t" << lastError << std::endl;
std::cout << std::endl;
}
int wmain(int argc, WCHAR* argv[])
{
CREDUI_INFO cuiInfo;
cuiInfo.cbSize = sizeof(CREDUI_INFO);
cuiInfo.hbmBanner = nullptr;
cuiInfo.hwndParent = nullptr;
cuiInfo.pszCaptionText = L"CaptionText";
cuiInfo.pszMessageText = L"MessageText";
DWORD dwAuthError = 0;
ULONG dwAuthPackage = 0;
LPVOID outCredBuffer = nullptr;
ULONG outCredBufferSize = 0;
BOOL credSaveCheckbox = false;
DWORD dwError = 0;
DWORD lastError = 0;
dwError = CredUIPromptForWindowsCredentials(
&cuiInfo,
dwAuthError,
&dwAuthPackage,
nullptr,
NULL,
&outCredBuffer,
&outCredBufferSize,
&credSaveCheckbox,
CREDUIWIN_CHECKBOX | CREDUIWIN_GENERIC);
if (dwError == ERROR_SUCCESS)
{
DWORD maxUserNameSize = CREDUI_MAX_USERNAME_LENGTH;
DWORD maxDomainNameSize = CREDUI_MAX_DOMAIN_TARGET_LENGTH;
DWORD maxPasswordLength = CREDUI_MAX_PASSWORD_LENGTH;
LPWSTR szUserName = new WCHAR[maxUserNameSize];
LPWSTR szDomain = new WCHAR[maxDomainNameSize];
LPWSTR szPassword = new WCHAR[maxPasswordLength];
DWORD dwCredBufferSize = outCredBufferSize; //ULONG to DWORD
DWORD lastError = 0;
dwError = CredUnPackAuthenticationBuffer(
CRED_PACK_GENERIC_CREDENTIALS,
outCredBuffer,
dwCredBufferSize,
szUserName,
&maxUserNameSize,
szDomain,
&maxDomainNameSize,
szPassword,
&maxPasswordLength
);
lastError = GetLastError();
//Check for error
if (dwError == FALSE)
{
DisplayConsoleError(L"Blah", L"CredUnPackAuthenticationBuffer", lastError);
}
else
{
std::wcout << L"username " << szUserName << std::endl;
std::wcout << L"domain " << szDomain << std::endl;
std::wcout << L"password " << szPassword << std::endl;
}
}
else
{
lastError = dwError;
}
SecureZeroMemory(outCredBuffer, outCredBufferSize);
CoTaskMemFree(outCredBuffer);
return lastError;
}