Here is the solution that works for me on most wifi with portals.
Find mac address of the device you want to give access to. Also find your laptops mac address and save it.
Use some method to “spoof” your laptops wifi mac address to the mac address of the device.
Ive used http://www.macspoofer.com/ , there are plenty of tools and some terminal commands that work.
Connect to wifi and accept terms and conditions from your laptop with the changes mac address.
Revert/change your laptop back to original mac address.
Connect to wifi with your device. It should be pre-author based on mac address.
Let me know if you have any questions.