Comcast customers get a nice benefit: wherever there is an SSID of xfinitywifi, you can attach to it, enter your Comcast user/password credentials and get free WIFI. The catch is that your device has to have the ability to display a browser so you can actually enter your user/password credentials.
But once your device is authenticated, you attach to another xfinitywifi SSID in another place without having to enter your credentials.
However, this does not work for most smart TVs or other simple devices (i.e., ones that do not have a browser). So you cannot use xfinitywifi.
Comcast stores the MAC address of each device that was authenticated. Once that MAC address is stored, it is authenticated and does not have to enter a user/password. The trick is to get that MAC address stored in Comcast's database on your account.
Comcast customers can go here to see what MAC addresses are setup for xfinitywifi.
These steps have been blanked out to avoid certain legal issues.