<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\UnifiedRoleAssignment;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new UnifiedRoleAssignment();
$requestBody->setPrincipalId('679a9213-c497-48a4-830a-8d3d25d94ddc');
$requestBody->setRoleDefinitionId('ae79f266-94d4-4dab-b730-feca7e132178');
$requestBody->setAppScopeId('/AccessPackageCatalog/beedadfe-01d5-4025-910b-84abb9369997');
$result = $graphServiceClient->roleManagement()->entitlementManagement()->roleAssignments()->post($requestBody)->wait();