<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Models\TokenLifetimePolicy;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new TokenLifetimePolicy();
$requestBody->setDefinition(['{\"TokenLifetimePolicy\":{\"Version\":1,\"AccessTokenLifetime\":\"8:00:00\"}}', ]);
$requestBody->setDisplayName('Contoso token lifetime policy');
$requestBody->setIsOrganizationDefault(true);
$result = $graphServiceClient->policies()->tokenLifetimePolicies()->post($requestBody)->wait();