Steffen

...
#include <afxinet.h>
#include <regex>

...

void CwebsiteloginDlg::OnBnClickedButton1()
{
    using namespace std::tr1;

    CInternetSession internetSession;
    CString html;

    do
    {
        char tempRead[8192];

        // Fetch the main page (to find the sign-in page's URL)
        CHttpFile* f = static_cast<CHttpFile*>(internetSession.OpenURL(
            _T("http://answers.yahoo.com"),
            1,
            INTERNET_FLAG_TRANSFER_ASCII | INTERNET_FLAG_RELOAD | INTERNET_FLAG_DONT_CACHE));
        while (UINT numRead = f->Read(tempRead, _countof(tempRead) - 1))
        {
            tempRead[numRead] = '\0';
            html += tempRead;
        }

        f->Close();
        delete f;

        TCHAR* html_c = html.GetBuffer(html.GetLength());

        match_results<const TCHAR*> matches;
        basic_regex<TCHAR> pattern(_T("<a href=\"([^\"]+)\">Sign In</a>"));
        if (!regex_search(html_c, matches, pattern))
        {
            html.ReleaseBuffer();
            AfxMessageBox(_T("Did not find the sign-in URL."));
            break;
        }

        html.ReleaseBuffer();

        // Found the sign-in URL
        CString signinUrl(matches[1].first, matches[1].length());

        // Fetch the sign-in page
        f = static_cast<CHttpFile*>(internetSession.OpenURL(
            signinUrl,
            1,
            INTERNET_FLAG_TRANSFER_ASCII | INTERNET_FLAG_RELOAD | INTERNET_FLAG_DONT_CACHE));
        html.Empty();
        while (UINT numRead = f->Read(tempRead, _countof(tempRead) - 1))
        {
            tempRead[numRead] = '\0';
            html += tempRead;
        }

        // We're now on the sign-in page
        // We need to retrieve the info need to make another POST request (to do the actual sign-in)
        // If you look in the HTML document's source code, you can see the sign-in form and a field called ".challenge"
        // My guess is that you will need to post that data along with the other fields
        // Pay attention to the fields called "login" and "passwd"

        f->Close();
        delete f;

    } while (false);

    internetSession.Close();
}