"CHANGE USER" OPI call

Regarding "BECOME USER" privilege and upicui() function (UPI Change User Id):
There's a barely known OPI call "CHANGE USER", which is similar in a way to *NIX su. It is known to be used at least by IMP utility.
A caller should be logged in as a user with "BECOME USER" privilege and call upicui() to change it.
Here is sample code that illustrates it, it uses some ancient OCI API (OCI7, if I'm correct).
Here is my sample code which calls upicui() function in current OCI API.
All we need is to convert service handle to "hst" value needed by upicui() - using internal function kpusvc2hst() - and then call upicui().
This code snippet was successfully tried under win32 10.2 and 11. Change SID, USERNAME, PASSWORD and USERNAME2 before compiling.

#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <windows.h>

#include "oci.h"

typedef int (__cdecl *UPICUI)(int, int, const char *, int); 
typedef int (__cdecl *KPUSVC2HST)(OCISvcCtx *, OCIError *, int *, int); 

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

  OCIEnv *myenvhp;       /* the environment handle */
  OCIServer *mysrvhp;    /* the server handle */
  OCIError *myerrhp;     /* the error handle */
  OCISession *myusrhp;   /* user session handle */
  OCISvcCtx *mysvchp;    /* the  service handle */
  OCIStmt *stmt;
  OCIDefine *dfn;
  char	buf[10240];
  HMODULE oraclient;
  UPICUI upicui;
  KPUSVC2HST kpusvc2hst;
  int hst;

#define SID "orcl"

  assert (OCIEnvCreate (&myenvhp, OCI_THREADED|OCI_OBJECT, 0, 0, 0, 0, 0, 0)==0);

  assert (OCIHandleAlloc (myenvhp, (dvoid**)&mysrvhp, OCI_HTYPE_SERVER, 0, 0)==0);

  assert (OCIHandleAlloc (myenvhp, (dvoid**)&myerrhp, OCI_HTYPE_ERROR, 0, 0)==0);

  assert (OCIServerAttach (mysrvhp, myerrhp, (const OraText *)SID, strlen (SID), OCI_DEFAULT)==0);

  assert (OCIHandleAlloc (myenvhp, (dvoid**)&mysvchp, OCI_HTYPE_SVCCTX, 0, 0)==0);

  assert (OCIAttrSet (mysvchp, OCI_HTYPE_SVCCTX, mysrvhp, 0, OCI_ATTR_SERVER, myerrhp)==0);

  assert (OCIHandleAlloc (myenvhp, (dvoid**)&myusrhp, OCI_HTYPE_SESSION, 0, 0)==0);

  assert (OCIHandleAlloc (myenvhp, (dvoid**)&stmt, OCI_HTYPE_STMT, 0, 0)==0);

#define USERNAME "sys"
#define PASSWORD "qq"

  assert (OCIAttrSet (myusrhp, OCI_HTYPE_SESSION, USERNAME, strlen(USERNAME), OCI_ATTR_USERNAME, myerrhp)==0);

  assert (OCIAttrSet (myusrhp, OCI_HTYPE_SESSION, PASSWORD, strlen(PASSWORD), OCI_ATTR_PASSWORD, myerrhp)==0);

  assert (OCISessionBegin (mysvchp, myerrhp, myusrhp, OCI_CRED_RDBMS, OCI_SYSDBA)==0);

  oraclient=LoadLibrary ("oraclient11.dll");
  assert (oraclient!=NULL);
  upicui=(UPICUI)GetProcAddress (oraclient, "upicui"); assert (upicui!=NULL);
  kpusvc2hst=(KPUSVC2HST)GetProcAddress (oraclient, "kpusvc2hst"); assert (kpusvc2hst!=NULL);

  printf ("kpusvc2hst -> %d\n", (kpusvc2hst) (mysvchp, myerrhp, &hst, 1));

#define USERNAME2 "SCOTT"

  printf ("upicui -> %d\n", (upicui)( hst, 0, USERNAME2, strlen (USERNAME2) ));

  assert (OCIAttrSet (mysvchp, OCI_HTYPE_SVCCTX, myusrhp, 0, OCI_ATTR_SESSION, myerrhp)==0);

#define STMT "select user from dual"

  assert (OCIStmtPrepare (stmt, myerrhp, (const OraText *)STMT, strlen (STMT), OCI_NTV_SYNTAX, OCI_DEFAULT)==0);

  assert (OCIDefineByPos (stmt, &dfn, myerrhp, 1, buf, 10240, SQLT_STR, 0, 0, 0, OCI_DEFAULT)==0);

  assert (OCIStmtExecute (mysvchp, stmt, myerrhp, 1,  0, NULL, NULL, OCI_DEFAULT)==0);

  printf ("%s\n", buf);
};

Update:
How to do the same in Linux:
http://arkzoyd.blogspot.com/2009/02/become-user-sous-linux.html