It's called 'captive portal'. Try dd-wrt, with a compatible wifi router.

From: Dave Cramer
Sent: ‎3/‎7/‎2015 10:27 AM
To: GTALUG
Subject: [GTALUG] Open source router with http login

I have a need for a router like they have at hotels where people need to login to get a connection.

Is there anything a)small, and b) open source available ?

Dave Cramer