<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\CustomSecurityAttributeDefinition;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new CustomSecurityAttributeDefinition();
$requestBody->setDescription('Target completion date (YYYY/MM/DD)');
$result = $graphServiceClient->directory()->customSecurityAttributeDefinitions()->byCustomSecurityAttributeDefinitionId('customSecurityAttributeDefinition-id')->patch($requestBody)->wait();