Get all repos a Github app has access to within an organisation, given the app id, installation id and private key.

get_repos_of_app_within_org.php

<?php

/**
 * composer require knplabs/github-api:^3.16 lcobucci/jwt:^4.1
 */

require 'vendor/autoload.php';

use Github\Client;
use Github\HttpClient\Builder;
use Github\AuthMethod;
use Github\ResultPager;
use Lcobucci\JWT\Configuration;
use Lcobucci\JWT\Encoding\ChainedFormatter;
use Lcobucci\JWT\Signer\Key\LocalFileReference;
use Lcobucci\JWT\Signer\Rsa\Sha256;

$appId = '';
$installationId = '';
$orgName = '';
$privateKeyPath = '';

$builder = new Builder();
$github = new Client($builder, 'machine-man-preview');

$config = Configuration::forAsymmetricSigner(
    new Sha256(),
    LocalFileReference::file($privateKeyPath),
    LocalFileReference::file($privateKeyPath)
);

$now = new \DateTimeImmutable();
$jwt = $config->builder(ChainedFormatter::withUnixTimestampDates())
    ->issuedBy($appId)
    ->issuedAt($now)
    ->expiresAt($now->modify('+1 minute'))
    ->getToken($config->signer(), $config->signingKey())
;

$github->authenticate($jwt->toString(), null, AuthMethod::JWT);

$tokenData = $github->apps()->createInstallationToken($installationId);
$installationToken = $tokenData['token'];

$github->authenticate($installationToken, null, AuthMethod::ACCESS_TOKEN);

$pager = new ResultPager($github);
$repositories = $pager->fetchAll(
    $github->organizations(),
    'repositories',
    [$orgName]
);

foreach ($repositories as $repo) {
    echo $repo['full_name'] . PHP_EOL;
}