OpenBSD, WPA WiFi Connection with Website Authentication

I travel a lot on buses, most of which have some sort of WiFi on board. The usual way to connect to them using an automatic connection manager like Wicd is to select a network, and then when the browser starts up, additional authentication happens and I'm done. But OpenBSD does not have such a manager, so I came to use it as a standard method as well ifconfig

. In the standard case where I have for example WEP2 encryption and password authentication to get started:

ifconfig iwn0 nwid <network_id> wpakey <password>

      

        
        
        
      

    

and after that:

dhclient iwn0

      

        
        
        
      

    

The question is how to connect in case of a bus where there is no password? So far, I've tried a few things, like not specifying a password at all, or providing an empty password (rejected immediately), but they all produced output like this:

iwn0: no link ............. sleeping

      

        
        
        
      

    

at startup dhclient

.