Stream xfinity on Apple TV from non-xfinity internet provider?

I have been an xfinity cable TV subscriber “forever.”  My internet provider (via DSL) has been my local phone company for even longer. I have had reason to stream xfinity tv content from the internet through either my iPhone or iPad — using the xfinity streaming app —  or a Mac — using the xfinity website — air playing through a 1st Gee Apple TV, all of which has worked fine.  I recently acquired a new Apple TV and installed the xfinity streaming app on it.  I discovered to my great disappointment that it appears I cannot make the xfinity app work on the Apple TV because I am not an xfinity internet customer. Can anyone authoritatively confirm that is true, and WHY, but if it is not true tell me what I might be doing wrong?

(I tried searching the forums for an answer to my question but couldn’t really find one.)