Add Private Webcal to outlook.com

I want to add a Webcal, which is Password protected to my outlook.com account. I need to do this because of my job so i have it synced to my tablet and my windows phone. But it doesn't work. It always returns with an error, that i can't add a private callendar. I can add it to outlook 2013, but this doesnt help me because i cant sync it to my windows phone 8. So how can I add this calendar? I need to do this and it has to be possible!