<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\ExternalAuthenticationMethod;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new ExternalAuthenticationMethod();
$requestBody->setOdataType('#microsoft.graph.externalAuthenticationMethod');
$requestBody->setConfigurationId('26310fee-860b-4eab-8749-ab730dcf335e');
$requestBody->setDisplayName('Adatum');
$result = $graphServiceClient->users()->byUserId('user-id')->authentication()->externalAuthenticationMethods()->post($requestBody)->wait();