this is for our thesis project. we proposed to study the Wi-Fi security in most related to the users.
closed as not a real question by Rory Alsop♦ Apr 2 '12 at 12:25
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The usual method is called "Captive Portal".
When the client first connects, all web page requests are intercepted and sent to the the login page instead. (Any non-web traffic sent at this point is dropped.)
One the user authenticates, the access point notes that it's authenticated, and subsequently allows traffic from that connection through to the Internet.