在Visual C ++中获取SMTP服务器证书（端口587，STARTTLS）

Question

我认为这可以通过openssl完成，但没有任何方法可以做到吗？

如果使用以下代码连接到具有隐式SSL的端口（例如，smtp.gmail.com，端口465），我可以获得证书没问题。

// Convert the server name to a wide string
USES_CONVERSION;
LPWSTR lpServerName = A2W(szServer);

BOOL bResults = FALSE;
HINTERNET   hSession = NULL, hConnect = NULL, hRequest = NULL;

hSession = WinHttpOpen( L"my app", 
    WINHTTP_ACCESS_TYPE_DEFAULT_PROXY,
    WINHTTP_NO_PROXY_NAME, 
    WINHTTP_NO_PROXY_BYPASS, 0 );

if( hSession )
    hConnect = WinHttpConnect( hSession,  
    lpServerName,
    PortNum, 0 );

if( hConnect )
    hRequest = WinHttpOpenRequest( hConnect, L"GET",  
    NULL,
    NULL, WINHTTP_NO_REFERER, 
    WINHTTP_DEFAULT_ACCEPT_TYPES, 
    WINHTTP_FLAG_SECURE );

if( hRequest )
    bResults = WinHttpSendRequest( hRequest,
    WINHTTP_NO_ADDITIONAL_HEADERS, 0,
    WINHTTP_NO_REQUEST_DATA, 0, 
    0, 0 );

if(hRequest)
{
    // Okay, the connection and request succeeded, now try to get the certificate chain
    PCCERT_CONTEXT pCert=NULL;
    DWORD dwSize = sizeof(pCert);
    BOOL res = WinHttpQueryOption(hRequest,
        WINHTTP_OPTION_SERVER_CERT_CONTEXT,
        &pCert,
        &dwSize);   

    if (res) 
    {
        // Do stuff
    }
}