Logout proxy authentication

Hello,

in our school we are using iPads with a external proxyserver, which filters the internet. To get into the internet, the student must be login with a authentication for this server (in Safari comes a popup).

Now we don't know, how the student can logout after the session. Is there a option, to restore this option, that the next student can log in?

We are using also a mdm in our network, is there a option to found?

Thanks!