<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Models\Ediscovery\UnifiedGroupSource;
use Microsoft\Graph\Beta\Generated\Models\Group;
use Microsoft\Graph\Beta\Generated\Models\Ediscovery\SourceType;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new UnifiedGroupSource();
$group = new Group();
$group->setMail('SecretGroup@contoso.com');
$requestBody->setGroup($group);
$requestBody->setIncludedSources(new SourceType('mailbox, site'));
$result = $graphServiceClient->compliance()->ediscovery()->cases()->byCaseId('case-id')->custodians()->byCustodianId('custodian-id')->unifiedGroupSources()->post($requestBody)->wait();