You could find out the IP range of the free wifi by connecting a different device (Notebook or Smartphone) to it and look for the settings this device shows.
From what i see the XFINITY secure hotspot uses EAP which requires username and password while open xfinitywifi uses portal page once you are connected if mac address is not authenticated
When i try connect through Gl.Inet web page to XFINITY secure hotspot refuses to connect and log shows Reason:23=IEEE8021X FAILED
That link for xfinitywifi not XFINITY is the secure hotspot that uses EAP authentication. GL.inet router works fine for open xfinitywifi but the secure XFINITY hotspot it won’t connect to.