You either open a port, or employ a third party (even if you run that yourself), no in-between. If you'd like a secure setup, I'd advise a generic WiFi camera,

You either open a port, or employ a third party (even if you run that yourself), no in-between. If you'd like a secure setup, I'd advise a generic WiFi camera, accessible only on your LAN, and setting up OpenVPN or similar, to connect to your home network. This way you need to only trust your chosen VPN implementation, and I'd wager they are pretty secure.