No there isn't. Xfinity doesn't want their customers to enjoy the benefits of paid premium subscriptions like other providers such as Dish and Directv.
On a side note, Xfinity won't let you authenticate through the NFL network app either.
Furthermore, xfinity has the lowest premium channel hd selection out of any provider. Directv and dish have just about every single starz channel in hd where as xfinity only has 2 or 3. The same can be said for hbo and showtime. Xfinity does not want their customers to enjoy hd or enjoy the benefits of being able to authenticate via the starz app like dish and directv customers.