When you create a Web Authentication WLAN on your controller, users authenticate (open), associate, receive an IP address, then get blocked until they open a browser. The DNS query they initiate goes through the controller, and upon receiving the DNS answer, the controller redirects the user to the Web Authentication page, were credentials have to be entered...
It is this last part that I was looking at a few days ago... how are these credentials exchanged between the controller and the client? Post? Pull?
Actually the process is a PAP! When you enter the username and password, the username and password pair is sent over the air with a PAP Access Request message.
The controller validates the username and password pair, from a local list or through a RADIUS server, and grants (or refuses) access. Of course, PAP is a very weak protocol, and you might have jumped on chair while reading this... so is this process so weak that anyone could eavesdrop and read the sent username and password?
Not really, look at this capture of such an exchange. Client is 10.1.1.57 and Virtual gateway 188.8.131.52:
As you might have guessed, the process occurs via HTTPS, so the user credentials are protected by the TLS session... not very easy to hack.
Nevertheless, you could argue that if you were to sniff the exchange, you might be able to break it offline, and that PAP is therefore bad.
Okay, not a problem. You can replace PAP with CHAP. With CHAP, the username is sent through the TLS tunnel, and then the RADIUS or the controller returns a challenge. The client browser encrypts the challenge with the password, and sends the result back. The controller (or RADIUS) does the same on its side. If both results are the same, both sides used the same password and the authentication is successful without the password having been sent.
How do you change Web authentication from PAP to CHAP? Strangely enough, in Controller > General.
The controller natively supports these three modes. If you use an external RADIUS server, make sure it supports them. ACS supports both PAP and CHAP (but not MD5-CHAP as far as I know).
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