Activate and configure XFi router/bridge/modem from browser connection

Hello.

I am not so interested in using the XFinity app to activate and configure my router/bridge/modem.  I would like to connect to it directly from my computer with an ethernet cable via its IP address and configure it that way by talking to the firmware directly.  In the manner that was common for connecting to network hardware in the past.

How do I do this?