SEC_WINNT_AUTH_IDENTITY creation (SSPI)

Question

i'm trying to create an SEC_WINNT_AUTH_IDENTITY to use into a call to AcquireCredentialsHandle in order to get credentials for this identity. However i struggle creating the Authenfication date.

Here is the code used to create the struct :

#define SECURITY_WIN32
#include <Windows.h>
#include <sspi.h>


int main(int argc, char* argv[]) {

SEC_WINNT_AUTH_IDENTITY AuthId;
char* login = "login";
char* domain = "mydomain.com";
char* password = "pass";

AuthId.User = login;
AuthId.UserLength = strlen(login);
AuthId.Domain = domain;
AuthId.DomainLength = strlen(domain);
AuthId.Password = password;
AuthId.PasswordLength = strlen(password);
AuthId.Flags = SEC_WINNT_AUTH_IDENTITY_ANSI;

//Here the call to AcquireCredentialHandle and the end of the program
}

The problem is that the struct want unsigned short __RPC_FAR *User but i can't find any info on this and how i'm supposed to pass it strings. The examples i found ont Internet are all using strings directly.

score 2 · Accepted Answer · answered Nov 14 '15 at 16:22

Some experience in ODBC helped me in this situation. However, it won't work for Unicode passwords, and I do not need it for now. But it would be nice if someone will give a hint.

Well, here is my solution. I've created helper class:

Header:

class StringParam
{
public:
    StringParam();
    StringParam(const std::wstring& val);
    StringParam(const std::string& val);
    virtual ~StringParam();

    unsigned short* GetBuffer() const;
    unsigned long   GetBufferLength() const;
    unsigned long   GetLength() const;
private:
    unsigned short* buffer;
    unsigned long   bufferLength;
};

Implementation:

StringParam::StringParam():
    buffer(NULL),
    bufferLength(0)
{
}

StringParam::StringParam(const std::wstring& val):
    StringParam()
{
    size_t len = val.size(); // .length() is the same
    bufferLength = sizeof(unsigned short) * (len + 1);
    unsigned short* buf = new unsigned short[len + 1];
    memset(buf, 0, bufferLength);
    int i = 0;
    for (wchar_t c: val)
        buf[i++] = (unsigned short)c;

    buffer = reinterpret_cast<unsigned short*>(buf);
}

StringParam::StringParam(const std::string& val):
    StringParam()
{
    size_t len = val.size(); // .length() is the same
    bufferLength = sizeof(unsigned short) * (len + 1);
    unsigned short* buf = new unsigned short[len + 1];
    memset(buf, 0, bufferLength);
    int i = 0;
    for (char c: val)
        buf[i++] = (unsigned short)c;

    buffer = reinterpret_cast<unsigned short*>(buf);
}

StringParam::~StringParam()
{
    if (buffer)
    {
        delete[] buffer;
        buffer = NULL;
        bufferLength = 0;
    }
}

unsigned short* StringParam::GetBuffer() const
{
    return buffer;
}

unsigned long StringParam::GetBufferLength() const
{
    return bufferLength;
}

unsigned long StringParam::GetLength() const
{
    return bufferLength / sizeof(unsigned short);
}

Usage:

SECURITY_STATUS res;

// Aquire credentials
CredHandle              credentials;
TimeStamp               credentialsExpiryTime;

SEC_WINNT_AUTH_IDENTITY userIdentity;
StringParam prmDomain("domain.com");
StringParam prmUser("username");
StringParam prmPassword("password#1");
// wstring version will also work:
//StringParam prmDomain(L"domain.com");
//StringParam prmUser(L"username");
//StringParam prmPassword(L"password#1");

userIdentity.Domain = prmDomain.GetBuffer();
userIdentity.DomainLength = prmDomain.GetLength();
userIdentity.User = prmUser.GetBuffer();
userIdentity.UserLength = prmUser.GetLength();
userIdentity.Password = prmPassword.GetBuffer();
userIdentity.PasswordLength = prmPassword.GetLength();
userIdentity.Flags = SEC_WINNT_AUTH_IDENTITY_UNICODE;
res = AcquireCredentialsHandle(NULL, L"Kerberos", SECPKG_CRED_INBOUND, NULL, &userIdentity, NULL, NULL, &credentials, &credentialsExpiryTime);

Works just fine for me. The trick is that wchar_t is 4 bytes long. But SSPI uses UTF-16. In ODBC Unicode characters converted from wstring worked, but here something is different.

why not using wcslen() for counting the size of a wstring? I've used it and it works without problems — madduci, Jan 28 '16 at 09:51
another task is to convert 4 bytes to 2 bytes per every character in string — Viktor, Jan 30 '16 at 11:28
If using Visual Studio, right click Project -> properties -> Advanced -> Character Set = Use Multi-Byte Character Set. — Juan Rojas, Jan 07 '20 at 20:49

SEC_WINNT_AUTH_IDENTITY creation (SSPI)

1 Answers1