public function acs()
    {
        $auth = Injector::inst()->get('SAMLHelper')->getSAMLAuth();
        $auth->processResponse();

        $error = $auth->getLastErrorReason();
        if (!empty($error)) {
            SS_Log::log($error, SS_Log::ERR);
            Form::messageForForm("SAMLLoginForm_LoginForm", "Authentication error: '{$error}'", 'bad');
            Session::save();
            return $this->getRedirect();
        }

        if (!$auth->isAuthenticated()) {
            Form::messageForForm("SAMLLoginForm_LoginForm", _t('Member.ERRORWRONGCRED'), 'bad');
            Session::save();
            return $this->getRedirect();
        }

        $decodedNameId = base64_decode($auth->getNameId());
        // check that the NameID is a binary string (which signals that it is a guid
        if (ctype_print($decodedNameId)) {
            Form::messageForForm("SAMLLoginForm_LoginForm", "Name ID provided by IdP is not a binary GUID.", 'bad');
            Session::save();
            return $this->getRedirect();
        }

        // transform the NameId to guid
        $guid = LDAPUtil::bin_to_str_guid($decodedNameId);
        if (!LDAPUtil::validGuid($guid)) {
            $errorMessage = "Not a valid GUID '{$guid}' recieved from server.";
            SS_Log::log($errorMessage, SS_Log::ERR);
            Form::messageForForm("SAMLLoginForm_LoginForm", $errorMessage, 'bad');
            Session::save();
            return $this->getRedirect();
        }

        // Write a rudimentary member with basic fields on every login, so that we at least have something
        // if LDAP synchronisation fails.
        $member = Member::get()->filter('GUID', $guid)->limit(1)->first();
        if (!($member && $member->exists())) {
            $member = new Member();
            $member->GUID = $guid;
        }

        $attributes = $auth->getAttributes();

        foreach ($member->config()->claims_field_mappings as $claim => $field) {
            if (!isset($attributes[$claim][0])) {
                SS_Log::log(
                    sprintf(
                        'Claim rule \'%s\' configured in LDAPMember.claims_field_mappings, but wasn\'t passed through. Please check IdP claim rules.',
                        $claim
                    ), SS_Log::WARN
                );

                continue;
            }

            if(count($attributes[$claim]) > 1) {
                $member->$field = $attributes[$claim];
            } else {
                $member->$field = $attributes[$claim][0];
            }
        }

        $member->SAMLSessionIndex = $auth->getSessionIndex();

        // This will trigger LDAP update through LDAPMemberExtension::memberLoggedIn.
        // The LDAP update will also write the Member record. We shouldn't write before
        // calling this, as any onAfterWrite hooks that attempt to update LDAP won't
        // have the Username field available yet for new Member records, and fail.
        // Both SAML and LDAP identify Members by the GUID field.
        $member->logIn();

        return $this->getRedirect();
    }