How To Handle Invalid Certificate Authority Error with WinInet

MORE INFORMATION

This error occurs when the client does not know about the certificate authority that issued the server certificate. The problem may be corrected by installing the certificate authority's root certificate. A list of all installed certificates can be viewed from Internet Explorer. From the View menu, click Internet Options, click the Content tab, and click Authorities.

It is possible to bypass this error in WinInet application without installing a certificate. There are two methods of handling this error. You can use code similar to the following.

Method 1. With a UI (a message box similar to Internet Explorer is generated):

   ...
   Again:
   if (!HttpSendRequest (hReq,...))
       dwError = GetLastError ();

   if (dwError == ERROR_INTERNET_INVALID_CA)
   {
       // Make sure to check return code from InternetErrorDlg
       // user may click either OK or Cancel. In case of Cancel
       // request should not be resumbitted.
       InternetErrorDlg (GetDesktopWindow(),
                         hReq,
                         ERROR_INTERNET_INVALID_CA,
                         FLAGS_ERROR_UI_FILTER_FOR_ERRORS |
                         FLAGS_ERROR_UI_FLAGS_GENERATE_DATA |
                         FLAGS_ERROR_UI_FLAGS_CHANGE_OPTIONS,
                         NULL);
      goto again;
   }
   ...
				

Method 2. Without a UI:

   ...
   Again:
   if (!HttpSendRequest (hReq,...))
      dwError = GetLastError ();
   if (dwError == ERROR_INTERNET_INVALID_CA)
   {
      DWORD dwFlags;
      DWORD dwBuffLen = sizeof(dwFlags);

      InternetQueryOption (hReq, INTERNET_OPTION_SECURITY_FLAGS,
            (LPVOID)&dwFlags, &dwBuffLen);

      dwFlags |= SECURITY_FLAG_IGNORE_UNKNOWN_CA;
      InternetSetOption (hReq, INTERNET_OPTION_SECURITY_FLAGS,
                            &dwFlags, sizeof (dwFlags) );
      goto again;
   }
   ...
				

Similar logic can be used with MFC WinInet classes. In this case, the following MFC methods correspond to the WinInet APIs used above:

• CInternetFile::SendRequest
• CInternetFile::QueryOption
• CInternetFile::SetOption
• CInternetFile::ErrorDlg

Please note that Visual C++ 5.0 is missing documentation on CInternetFile::ErrorDlg, CInternetFile::QueryOption, and CInternetFile::SetOption. See the Inet.cpp MFC source file for information how to use this method.

NOTE 1: InternetErrorDlg may return following values:

   ERROR_SUCCESS
   ERROR_CANCELLED
   ERROR_INTERNET_FORCE_RETRY.
				

The request should be resubmitted only when ERROR_INTERNET_FORCE_RETRY is returned. In Internet Explorer 4.0 and 4.01, however, the request must be resubmitted even when ERROR_SUCCESS is returned.

Microsoft has confirmed this to be a problem in InternetErrorDlg API. NOTE 2: SECURITY_FLAG_IGNORE_UNKNOWN_CA is not implemented in Internet Explorer 3.0 and 3.02.

InternetErrorDlg still works, however, with the following exception. The dialog box generated by this API does not allow ignore invalid certificate authority error; it is merely a notification to the user that page cannot be viewed.

NOTE 3: The option to ignore this error cannot be set before the error occurs. You must first attempt to send the request, receive the error, then set the option (or call InternetErrorDlg), and resubmit.