IHttpUser::GetImpersonationToken Method

Returns the user impersonation token.


virtual HANDLE GetImpersonationToken(  
) = 0;  


This method takes no parameters.

Return Value

A HANDLE that represents the impersonation token for the user; otherwise, NULL.


The SupportsIsInRole and IsInRole methods return FALSE and E_NOTIMPL, respectively, from the default implementation. Therefore, use the handle that is returned from either the GetImpersonationToken or GetPrimaryToken method for role-based authorization.

Notes for Implementers

IHttpUser implementers are responsible for resource management with this data; therefore, IHttpUser implementers must call CloseHandle on the handle when it is no longer needed.

Notes for Callers

IHttpUser implementers are responsible for resource management with this data; therefore, IHttpUser clients must not call CloseHandle on the returned handle when this data is no longer needed. Furthermore, clients must not change the state of the memory referenced by this handle, because an access violation will be thrown or the data will become invalid.


The following code example demonstrates how to create an HTTP module that clears the response headers and body and then returns user information to the client as an XML document.

#pragma warning( disable : 4290 )
#pragma warning( disable : 4530 )

#define _WINSOCKAPI_
#include <windows.h>
#include <io.h>
#include <sal.h>
#include <httpserv.h>

#include <string>
using namespace std;

#import "msxml6.dll"
using namespace MSXML2;

// The CConvert class mirrors the Convert class that is 
// defined in the .NET Framework. It converts primitives 
// and other data types to wstring types.
class CConvert
    // The ToString method converts a HANDLE to a wstring.
    // h: the HANDLE to convert to a wstring.
    // return: the HANDLE as a wstring.
    static wstring ToString(HANDLE h)
        // If the HANDLE is NULL, return the "NULL" string.
        if (NULL == h)
            return L"NULL";

        // If the HANDLE is not valid, return 
        // the INVALID_HANDLE_VALUE as a string.
        if (INVALID_HANDLE_VALUE == h)
            return L"INVALID_HANDLE_VALUE";

        // The HANDLE is valid.
        return L"valid";

    // The ToByteString converts a double-byte 
    // character string to a single-byte string.
    // str: the double-byte string to convert.
    // return: a single-byte string copied from str.
    static string ToByteString(const wstring& str)
        // Get the length of the 
        // double-byte string.
        size_t length = str.length();

        // Create a temporary char pointer.
        char* byteChar = new char[length+1];
        byteChar[0] = '\0';
        // Copy the double-byte character string
        // into the single-byte string.        
        size_t charsReturned = 0;
        wcstombs_s(&charsReturned, byteChar, 
                   length+1, str.c_str(), length+1);
        // Create a string to return.
        string retString = byteChar;
        // Delete the temporary string and
        // set that string to NULL.
        delete[] byteChar;
        byteChar = NULL;

        // Return the single-byte string.
        return retString;

// The CResponseWriter class writes 
// text to the response stream.
class CResponseWriter
    // Creates the CResponseWriter class.
    // response: the IHttpResponse 
    // pointer to write to.
    // throws: a _com_error exception if
    // the IHttpResponse pointer is NULL.
    CResponseWriter(IHttpResponse* response)
        throw (_com_error)
        // If the response is NULL,
        // throw an exception.
        if (NULL == response)

        // Set the internal response.
        m_response = response;

    // The destructor for the CResponseWriter
    // class. The CResponseWriter method 
    // sets the IHttpResponse pointer to NULL.
    virtual ~CResponseWriter()
        m_response = NULL;

    // The Write method writes the 
    // PCSTR to the response stream.
    // pszValue: the PCSTR to write.
    // throws: a _com_error if the 
    // Write method fails.
    void Write
        PCSTR pszValue        
    ) throw (_com_error)
        // The string must not be 
        // NULL, and its length must 
        // be greater than 0.
        if ((NULL == pszValue) || 
            (strlen(pszValue) < 1))            
            // Throw an invalid argument
            // exception.

        // Create a data chunk structure.
        HTTP_DATA_CHUNK dataChunk;
        // Set the chunk to a chunk in memory.
        dataChunk.DataChunkType = 

        // Set the chunk to 
        // the pszValue parameter.
        dataChunk.FromMemory.pBuffer = 
        // Set the chunk size 
        // to the pszValue length.
        dataChunk.FromMemory.BufferLength = 
        // Declare and initialize OUT 
        // parameters for the WriteEntityChunks 
        // method.
        DWORD pcbSent = 0;
        BOOL pfCompletionExpected = FALSE;

        // Write the entity chunks to
        // the response stream.
        HRESULT hr =

        // Throw an exception if the call
        // to WriteEntityChunks is not a 
        // success.

    // Tests an HRESULT for success.
    // hr: the HRESULT value to inspect.
    // throws: a _com_error if the HRESULT
    // parameter is not S_OK.
    static void ThrowOnFail(HRESULT hr)
        if (FAILED(hr))
            _com_error ce(hr);
            throw ce;
    // Specify the IHttpResponse
    // pointer to write to.
    IHttpResponse* m_response;

// The CUser class is the wrapper 
// class for an IHttpUser pointer.
class CUser
    // Creates the CUser class.
    // user: the IHttpUser pointer to reference.
    // throws: a _com_error exception if 
    // the IHttpUser parameter is NULL.
    CUser(IHttpUser* user)
        throw (_com_error)
        // Throw an exception if the 
        // IHttpUser parameter is NULL.
        if (NULL == user)
            _com_error ce(E_INVALIDARG);
            throw ce;

        // Call ReferenceUser, which increments
        // the reference count for the user.
        // Assign the user to m_user.
        m_user = user;

    // The CUser method is the public 
    // destructor for the CUser class.
    // The destructor calls the DereferenceUser
    // method on the IHttpUser pointer, and
    // sets that pointer to NULL.
    virtual ~CUser()
        // Call DereferenceUser on the m_user private 
        // data, which decrements the reference count
        // on m_user. An IHttpUser will be deleted when 
        // its reference count goes to 0.
        // Set the m_user data to NULL.
        m_user = NULL;

    // The CreateElement method converts 
    // the internal IHttpUser pointer and 
    // descendant data into an XML element.
    // doc: the MSXML2::IXMLDOMDocument3Ptr to use 
    // for creating elements and attributes.
    // return: a new IXMLDOMElementPtr pointer.
    // throws: a _com_error exception.
    MSXML2::IXMLDOMElementPtr CreateElement
        MSXML2::IXMLDOMDocument3Ptr doc
    ) const throw (_com_error)
        // Create a new XML element to return.
        MSXML2::IXMLDOMElementPtr userElement = 

        // Call the GetImpersonationToken 
        // method on the IHttpUser pointer.
        HANDLE impersonationTokenHANDLE = 

        // Convert the HANDLE to a wstring.
        wstring impersonationToken =

        // Write an attribute to the 
        // userElement element.

        // Return the XML element.
        return userElement;
    // The AddAttribute method creates a new XML 
    // attribute and appends it to the element
    // parameter.
    // name: the name of the attribute.
    // text: the text value of the attribute.
    // element: the XML element to 
    // append the new attribute to.
    // doc: the XML document to use for
    // creating attributes.
    // return: a new IXMLDOMAttributePtr.
    // throws: a _com_error exception.
    static MSXML2::IXMLDOMAttributePtr AddAttribute
        const wstring& name,
        const wstring& text,
        MSXML2::IXMLDOMElementPtr element,
        MSXML2::IXMLDOMDocument3Ptr doc
    ) throw (_com_error)
        // Create an attribute with the name.
        MSXML2::IXMLDOMAttributePtr attribute = 
        // Set the text of the attribute to the text value.
        attribute->text = text.c_str();
        // Add the attribute to the passed element.
        // Return the new attribute to the caller.
        return attribute;
    // Specify the IHttpUser pointer 
    // to authenticate and authorize.
    IHttpUser* m_user;

// The CHttpResponseModule is a CHttpModule 
// class that handles response processing
// by creating a custom user and writing that
// user information to the response stream.
class CHttpResponseModule : public CHttpModule
    // The CHttpResponseModule method is the public
    // constructor for the CHttpResponseModule class.


    // The CHttpResponseModule method is 
    // the public virtual destructor for 
    // the CHttpResponseModule class.
    virtual ~CHttpResponseModule()


    // The OnSendResponse method is the method 
    // supporting the RQ_SEND_RESPONSE event type.
    // pHttpContext: the current IHttpContext pointer.
    // pProvider: the current IHttpEventProvider pointer.
        IN IHttpContext* pHttpContext,
        IN OUT ISendResponseProvider* pProvider
        // Call the UNREFERENCED_PARAMETER macro because
        // the ISendResponseProvider is never used.

        // If the IHttpContext is NULL, 
        if (NULL == pHttpContext)
            return RQ_NOTIFICATION_CONTINUE;

        // Retrieve the IHttpUser pointer 
        // from the IHttpContext pointer.
        IHttpUser* user = 

        // Retrieve the IHttpResponse pointer 
        // from the IHttpContext pointer.
        IHttpResponse* response = 

        // Both the IHttpUser and 
        // IHttpResponse pointers must 
        // not be NUL to continue
        // response processing.
        if ((NULL == user) || (NULL == response))
            return RQ_NOTIFICATION_CONTINUE;

        // Wrap calls in a try-catch 
        // statement as a _com_error 
        // exception might be thrown.
            // Create a CUser wrapper
            // for the IHttpUser pointer.
            CUser userWrapper(user);

            // Create a new XML document.

            // Get the user XML element from
            // the CUser class, and append 
            // this element to the XML document.
            MSXML2::IXMLDOMElementPtr userElement =
            // Create the string for writing 
            // the XML to the response stream.
            _bstr_t bstrXml = doc->xml;
            string xmlString = 
                "<?xml version=\"1.0\"?>" + bstrXml;

            // Reset the header for text/xml so that
            // browsers will display the XML correctly.
            HRESULT hr = 

            // Do not throw an exception here.
            // If the header cannot be set, then
            // the user should be able to view
            // the XML by selecting the
            // "View\Source" menu item.

            // Clear the response before writing
            // the XML data to the response.

            // Create a writer.
            CResponseWriter writer(response);

            // Write the XML to the 
            // response stream.
        catch (_com_error& ce)
            // Attempt to get the 
            // description of the error.
            _bstr_t description = 

            // Print the description if 
            // it is not empty.
            if (0 == description.length())
                description = ce.ErrorMessage();            
            // Set an error status on the 
            // IHttpResponse pointer.
            response->SetStatus(500, description, 0, ce.Error());

        // Return the RQ_NOTIFICATION_CONTINUE message.

// The CHttpResponseFactory class implements the 
// IHttpModuleFactory interface and creates and 
// sets a new CHttpResponseModule listener for 
// the RQ_SEND_RESPONSE event on the 
// IHttpModuleRegistrationInfo pointer.
class CHttpResponseFactory : public IHttpModuleFactory
    // The RegisterCHttpModule method creates a new 
    // CHttpResponseFactory pointer and sets this new 
    // CHttpResponseFactory pointer as the IHttpModuleFactory 
    // pointer on the IHttpModuleRegistrationInfo pointer.
    // dwServerVersion: the current server version.
    // pModuleInfo: the current 
    // IHttpModuleRegistrationInfo pointer.
    // pGlobalInfo: the current IHttpServer pointer.
    // return: the value returned from the the call to 
    // the SetRequestNotifications on the 
    // IHttpModuleRegistrationInfo pointer.
    static HRESULT RegisterCHttpModule
        DWORD dwServerVersion,
        IHttpModuleRegistrationInfo* pModuleInfo,
        IHttpServer* pGlobalInfo
        // Create a new CHttpResponseFactory pointer.
        CHttpResponseFactory* moduleFactory = 
            new CHttpResponseFactory;

        // Test for NULL on the new 
        // CHttpResponseFactory pointer.
        if (NULL == moduleFactory)
            // Return an out-of-memory error 
            // code if moduleFactory is NULL.

        // Set the request notifications for RQ_SEND_RESPONSE 
        // messages on the new CHttpResponseFactory pointer.
        return pModuleInfo->SetRequestNotifications

    // The GetHttpModule method creates a new 
    // CHttpResponseModule pointer and sets the 
    // new CHttpResponseModule on the ppModule parameter.
    // ppModule: the new CHttpResponseModule pointer to return.
    // pAllocator: currently unused.
    // return: ERROR_NOT_ENOUGH_MEMORY if the 
    // heap is exhausted; otherwise, S_OK.
        OUT CHttpModule** ppModule, 
        IN IModuleAllocator* pAllocator
        // Call the UNREFERENCED_PARAMETER macro with 
        // the IModuleAllocator pointer, because this
        // parameter is currently unused.

        // Set the dereferenced ppModule 
        // to a new CHttpResponseModule pointer.
        (*ppModule) = new CHttpResponseModule;

        // If the new CHttpResponseModule is 
        // NULL, return an error indicating 
        // that heap memory is exhausted.
        if (NULL == (*ppModule))

        // Return S_OK.
        return S_OK;

    // The Terminate method calls delete on this.
        delete this;

    // The CHttpResponseFactory method is the
    // protected constructor for the 
    // CHttpResponseFactory class.


    // The CHttpResponseFactory method is the 
    // protected virtual destructor for the
    // CHttpResponseFactory class.
    virtual ~CHttpResponseFactory()


// The RegisterModule method is the 
// main entry point for the DLL.
// dwServerVersion: the current server version.
// pModuleInfo: the current 
// IHttpModuleRegistrationInfo pointer.
// pGlobalInfo: the current IHttpServer pointer.
// return: the value returned by calling the static
// CHttpResponseFactory::RegisterCHttpModule method.
    DWORD dwServerVersion,
    IHttpModuleRegistrationInfo* pModuleInfo,
    IHttpServer* pGlobalInfo
    return CHttpResponseFactory::RegisterCHttpModule

The above code writes XML that is similar to the following to the response stream.

<?xml version="1.0" ?>  
<user impersonationToken="valid" />  

Your module must export the RegisterModule function. You can export this function by creating a module definition (.def) file for your project, or you can compile the module by using the /EXPORT:RegisterModule switch. For more information, see Walkthrough: Creating a Request-Level HTTP Module By Using Native Code.

You can optionally compile the code by using the __stdcall (/Gz) calling convention instead of explicitly declaring the calling convention for each function.


Type Description
Client - IIS 7.0 on Windows Vista
- IIS 7.5 on Windows 7
- IIS 8.0 on Windows 8
- IIS 10.0 on Windows 10
Server - IIS 7.0 on Windows Server 2008
- IIS 7.5 on Windows Server 2008 R2
- IIS 8.0 on Windows Server 2012
- IIS 8.5 on Windows Server 2012 R2
- IIS 10.0 on Windows Server 2016
Product - IIS 7.0, IIS 7.5, IIS 8.0, IIS 8.5, IIS 10.0
- IIS Express 7.5, IIS Express 8.0, IIS Express 10.0
Header Httpserv.h

See Also

IHttpUser Interface