IHttpRequest::GetClientCertificate Method

Article
06/14/2022

Retrieves the client certificate associated with the request.

Syntax

HRESULT GetClientCertificate(  
   OUT HTTP_SSL_CLIENT_CERT_INFO** ppClientCertInfo,  
   OUT BOOL* pfClientCertNegotiated  
);

Parameters

ppClientCertInfo
[OUT] A pointer to an HTTP_SSL_CLIENT_CERT_INFO structure.

pfClientCertNegotiated
[OUT] true if the client certificate has been negotiated already; otherwise, false. For more information, see the Remarks section.

Return Value

An HRESULT. Possible values include, but are not limited to, those in the following table.

Value	Definition
S_OK	Indicates that no error occurred, but does not guarantee that a certificate was found. For more information, see the Remarks section.
HRESULT_FROM_WIN32(ERROR_NOT_FOUND)	Indicates no client certificate was found. ERROR_NOT_FOUND is defined in Winerror.h.
ERROR_INVALID_PARAMETER	Indicates that the `ppClientCertInfo` or `pfClientCertNegotiated` parameter is NULL.

Remarks

A successful HRESULT does not guarantee that a client certificate was found. Developers must also verify that ppClientCertInfo is not NULL.

A pfClientCertNegotiated value of true does not guarantee that the ppClientCertInfo is not NULL.

Developers can use the GetClientCertificate method to retrieve the client certificate associated with the current request. After you call the GetClientCertificate method, the ppClientCertInfo parameter will contain a pointer to an HTTP_SSL_CLIENT_CERT_INFO structure, which will contain the client certificate if one is available or NULL if no certificate is available.

For URLs that do not require a client certificate, you can call the NegotiateClientCertificate method before you call GetClientCertificate to attempt a manual loading of the client certificate.

Example

The following example demonstrates how to get a pointer to the HTTP_SSL_CLIENT_CERT_INFO structure by implementing the CHttpModule::OnBeginRequest method.

void   checkForClientCert(IHttpContext*  pHttpContext)
{
   static long cnt;     
   // keep track of how many times we are called
   InterlockedIncrement (&cnt);  
   HRESULT hr = S_OK;
   IHttpRequest *pIHTTPR = pHttpContext->GetRequest();
   HTTP_REQUEST * pRawRequest = pIHTTPR->GetRawHttpRequest();
   HTTP_COOKED_URL hcu = pRawRequest->CookedUrl;

   // Send URL and count to the trace window
   TRC_MSGW_FULL(L"cnt = " << cnt << " URI: " << hcu.pFullUrl);

   // return immediately if not a HTTPS request
   if ( pRawRequest->pSslInfo == NULL ){
      TRC_MSG( "connection is not using SSL");
      return;
   }

   HTTP_SSL_CLIENT_CERT_INFO *pClientCertInfo=NULL;
   BOOL fccNeg;
   hr = pIHTTPR->GetClientCertificate(&pClientCertInfo,&fccNeg);

   // If you have not selected "Require Client Certificates" or called
   // NegotiateClientCertificate(), you  may get  ERROR_NOT_FOUND 

   if( hr == HRESULT_FROM_WIN32(ERROR_NOT_FOUND) ||
      pClientCertInfo == NULL ){
         TRC_HR_MSG(hr, "Cert not found" );
         return;
   }
   if(FAILED(hr)){
      LOG_ERR_HR("GetClientCertificate", hr);
      return;
   }	

   // You must verify pClientCertInfo != NULL

   if( fccNeg && pClientCertInfo != NULL){
      ULONG uSiz = pClientCertInfo->CertEncodedSize;
      TRC_MSG( "cert size: " << uSiz \
         << " Previously negotiated " << fccNeg );
      // compute the CRC check sum of the certificate
      unsigned long certCrc = genCRC(pClientCertInfo->pCertEncoded,
         pClientCertInfo->CertEncodedSize);
      TRC_MSG( "cert crc: " << certCrc );
   }
   else
      TRC_MSG( "No client certificate. fccNeg = " << fccNeg );
}

REQUEST_NOTIFICATION_STATUS
CMyHttpModule::OnBeginRequest(
                              IHttpContext*       pHttpContext,
                              IHttpEventProvider* // pProvider  
                              )
{
   checkForClientCert(pHttpContext);
   return RQ_NOTIFICATION_CONTINUE;
}

For more information about how to create and deploy a native DLL module, 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.

Requirements

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

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