How do you authenticate over http/web for Wi-Fi Access?

if 开发者_StackOverflow中文版you've used Wi-Fi at any cafe and other various hot spot places around town you might notice that sometimes in order to access the wi-fi you have to go to a login page or an agreements page before you can access the wifi network.

How do you set this up? What is necessary? Can you do this with any router? Can you do this with PHP? What is this technology called?

Let's put it simple, this is a functionality of the router, this cannot be done in PHP. You will need a "Captive Portal" in order to do the functionality you want to do.

One solution is to use an http proxy server such as Squid to authenticate users before proxying their http traffic to the internet. Here's an article that discusses the specifics:

http://www.askdavetaylor.com/configuring_squid_as_a_linux_proxy_server.html