'Authenticates the kiosk against the database.'

def requestAvatarId(self, credentials):

    for interface in self.credentialInterfaces:
        if interface.providedBy(credentials):
            break
    else:
        raise error.UnhandledCredentials()
    dbDeferred = self.runQuery(self.sql, (credentials.username,))
    deferred = Deferred()
    dbDeferred.addCallbacks(self._cbAuthenticate, self._ebAuthenticate, callbackArgs=(credentials, deferred), errbackArgs=(credentials, deferred))
    return deferred
