How to drive my credential provider with CredUIPromptForWindowsCredentials - winapi

Question

I've been working on a credential provider and I've been debugging it through logging. Recently learned about CredUIPromptForWindowsCredentials() API to be able to invoke it from other than login screen or remote desktop connection. The only way at this time I can seem to get my credential to display is to set the last param to CREDUIWIN_SECURE_PROMPT. I've tried various schemes of the flags with no luck. My CP works, that's not the problem. Problem is easier debugging. Only once have I had to go to rescue mode when I made my laptop unbootable. ;) The problem with using the CREDUIWIN_SECURE_PROMPT flag is that then I don't have access to the debugger because login takes over the screen and I can't get back to my debugger. I suppose the only workaround would be to remote debug on another machine with this API, but I'd prefer not to hassle with that.
My CP is registered at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\Credential Providers\{55157584-ff0f-48ce-9178-a4e290901663} and the default property is "MyCredProvider" (for this example). (GUID, prop name changed to protect the guilty. Also ignore LsaString where bad things would happen on a copy--of which I'm not doing.)
Any way to get my custom CP without using the secure prompt?
#include <windows.h>
#include <iostream>
#include <EvoApi.h>
#include <decrypt.h>
#include <atlbase.h>
#include <Lmwksta.h>
#include <StrSafe.h>
#include <LMAPIbuf.h>
#include <LMJoin.h>
#include <wincred.h>
#include <NTSecAPI.h>
#pragma warning(disable : 4996)
#pragma comment(lib, "netapi32.lib")
#pragma comment(lib, "credui.lib")
#pragma comment(lib, "secur32")
using namespace std;
template <size_t SIZE = 256>
struct LsaString : public LSA_STRING
{
LsaString()
{
MaximumLength = SIZE;
Length = 0;
Buffer = pBuf.get();
}
LsaString(LPCSTR pWhat)
{
MaximumLength = SIZE;
Length = 0;
Buffer = pBuf.get();
Init(pWhat);
}
void Init(LPCSTR pWhat)
{
size_t len = strlen(pWhat);
if (len >= SIZE)
throw;
strcpy(Buffer, pWhat);
Length = (USHORT) len;
}
unique_ptr<char[]> pBuf = make_unique< char[] >(SIZE);
};
int _tmain(int argc, wchar_t* argv[])
{
#if 1
wstring me(_T("MYLOGING"));
wstring url(_T("Header"));
wstring message(_T("Enter credentials for ..."));
CREDUI_INFOW credInfo;
credInfo.pszCaptionText = url.c_str();
credInfo.hbmBanner = nullptr;
credInfo.hwndParent = NULL;
credInfo.pszMessageText = message.c_str();
credInfo.cbSize = sizeof(CREDUI_INFOW);
ULONG authPackage = 0;
LSAHANDLE lsaHandle;
LsaConnectUntrusted(&lsaHandle);
LsaString<> lsaString("MyCredProvider");
//LsaString<> lsaString(MICROSOFT_KERBEROS_NAME_A); // works ... as far as finding in LsaLookupAuth...
//LsaString<> lsaString(NEGOSSP_NAME_A); // works ... as far as finding in LsaLookupAuth...
ULONG ulPackage = 0;
LsaLookupAuthenticationPackage(lsaHandle, &lsaString, &ulPackage);
void* pBlob;
ULONG blobSize = 0;
DWORD dwFlags = CREDUIWIN_GENERIC; //CREDUIWIN_SECURE_PROMPT
CredUIPromptForWindowsCredentials(&credInfo, 0, &ulPackage, NULL, 0, &pBlob, &blobSize, FALSE, dwFlags);
if (pBlob) CoTaskMemFree(pBlob);
return 0;
}