HOWTO: Getting User Name and Password in ISAPI or CGI App

• Microsoft Internet Information Server, version 1.0

SUMMARY

This article explains how to retrieve values for the user name and password in an ISAPI or CGI application.

MORE INFORMATION

The user name and password values can be retrieved in the ISAPI/CGI, according to the following rules.

The user name can only be retrieved when either Basic authentication scheme or Microsoft Windows NT Challenge/Response schemes are used. You can get the name by using the server variable, REMOTE_USER.

In ISAPI you can use GetServerVariable() API, and in CGI you can use getenv() C run-time function.

The following sample code can be used to get the server variable:

....

// This will fail with ERROR_INSUFFICIENT_BUFFER,
// since we supplied NULL buffer. As a result, dwLength will
// indicate the size of the buffer to allocate

                           "REMOTE_USER",
                           NULL,
                           &dwLength) )
{
    // Handle error other then ERROR_INSUFFICIENT_BUFFER here.

                                 "REMOTE_USER",
                                 lpszVar,
                                 &dwLength))
{
    // Handle error here

The user password can only be retrieved when Basic authentication scheme is used. The password is not available with the Windows NT Challenge/Response scheme, because the password never gets transmitted on the network.

To retrieve the password with the Basic authentication scheme, you need to parse it out from the HTTP_AUTHORIZATION server variable, which sets from HTTP Authorization header. HTTP_AUTHORIZATION has the following value:

   Basic xxxxxxxxxxxxxxx

Notes:

• The UUENCODE and UUDECODE routines are available from many public sources.
• The user password can not be retrieved via REMOTE_PASS server variable.
• In the IIS Filter application, the password (if available) can be retrieved in clear text from the HTTP_FILTER_AUTHENT structure:

        typedef struct _HTTP_FILTER_AUTHENT
        {
            CHAR *    pszUser;
            DWORD    cbUserBuff;
            CHAR *    pszPassword;
            DWORD    cbPasswordBuff;
        } HTTP_FILTER_AUTHENT, *PHTTP_FILTER_AUTHENT;