Auth_OpenID_GenericConsumer::_idResCheckForFields PHP Method

    function _idResCheckForFields($message)
    {
        $basic_fields = array('return_to', 'assoc_handle', 'sig', 'signed');
        $basic_sig_fields = array('return_to', 'identity');
        $require_fields = array(Auth_OpenID_OPENID2_NS => array_merge($basic_fields, array('op_endpoint')), Auth_OpenID_OPENID1_NS => array_merge($basic_fields, array('identity')));
        $require_sigs = array(Auth_OpenID_OPENID2_NS => array_merge($basic_sig_fields, array('response_nonce', 'claimed_id', 'assoc_handle', 'op_endpoint')), Auth_OpenID_OPENID1_NS => array_merge($basic_sig_fields, array('nonce')));
        foreach ($require_fields[$message->getOpenIDNamespace()] as $field) {
            if (!$message->hasKey(Auth_OpenID_OPENID_NS, $field)) {
                return new Auth_OpenID_FailureResponse(null, "Missing required field '" . $field . "'");
            }
        }
        $signed_list_str = $message->getArg(Auth_OpenID_OPENID_NS, 'signed', Auth_OpenID_NO_DEFAULT);
        if (Auth_OpenID::isFailure($signed_list_str)) {
            return $signed_list_str;
        }
        $signed_list = explode(',', $signed_list_str);
        foreach ($require_sigs[$message->getOpenIDNamespace()] as $field) {
            // Field is present and not in signed list
            if ($message->hasKey(Auth_OpenID_OPENID_NS, $field) && !in_array($field, $signed_list)) {
                return new Auth_OpenID_FailureResponse(null, "'" . $field . "' not signed");
            }
        }
        return null;
    }