Client.php

<?php
declare(strict_types=1);

namespace App\Service\ActivityPub;

use App\Entity\User;
use JsonException;
use Psr\Log\LoggerInterface;
use RuntimeException;
use Symfony\Contracts\HttpClient\Exception\ClientExceptionInterface;
use Symfony\Contracts\HttpClient\Exception\RedirectionExceptionInterface;
use Symfony\Contracts\HttpClient\Exception\ServerExceptionInterface;
use Symfony\Contracts\HttpClient\Exception\TransportExceptionInterface;
use Symfony\Contracts\HttpClient\HttpClientInterface;
use function base64_encode;
use function gmdate;
use function hash;
use function openssl_sign;
use function sprintf;
use const OPENSSL_ALGO_SHA256;

readonly class Client
{
    public function __construct(
        private HttpClientInterface $httpClient,
        private LoggerInterface $activitypubLogger
    ) {
    }

    /**
     * @param  string  $inboxUrl
     * @param  array<string, mixed>  $activity
     * @param  User|null  $user
     * @return void
     * @throws ClientExceptionInterface
     * @throws JsonException
     * @throws RedirectionExceptionInterface
     * @throws ServerExceptionInterface
     * @throws TransportExceptionInterface
     */
    public function sendToInbox(string $inboxUrl, array $activity, ?User $user = null): void
    {
        if ($user === null) {
            $this->activitypubLogger->debug('No user given', [
                'inboxUrl' => $inboxUrl,
                'message' => $activity,
            ]);

            return;
        }

        $body = json_encode($activity, JSON_THROW_ON_ERROR);
        $date = gmdate('D, d M Y H:i:s T');
        $digest = $this->generateDigest($body);
        $signature = $this->generateSignature($user, $inboxUrl, $date, $digest);

        $this->activitypubLogger->debug(__FUNCTION__, [
            'inboxUrl' => $inboxUrl,
            'message' => $activity,
            'Accept' => 'application/activity+json,application/ld+json,application/json',
            'Content-Type' => 'application/activity+json',
            'Digest' => "SHA-256=$digest",
            'Signature' => $signature,
            'Date' => $date,
        ]);

        try {
            $response = $this->httpClient->request('POST', $inboxUrl, [
                'body' => $body,
                'headers' => [
                    'Accept' => 'application/activity+json,application/ld+json,application/json',
                    'Content-Type' => 'application/activity+json',
                    'Digest' => "SHA-256=$digest",
                    'Signature' => $signature,
                    'Date' => $date,
                ],
            ]);
        } catch (TransportExceptionInterface $e) {
            $this->activitypubLogger->error($e->getMessage(), [
                'type' => $e::class,
                'message' => $e->getMessage(),
                'code' => $e->getCode(),
            ]);
            throw $e;
        }
        try {
            $content = $response->getContent();
        } catch (ClientExceptionInterface|RedirectionExceptionInterface|ServerExceptionInterface|TransportExceptionInterface $e) {
            /** @noinspection PhpUnhandledExceptionInspection */
            $content = $response->getContent(false);
            $this->activitypubLogger->error($e->getMessage(), [
                'type' => $e::class,
                'message' => $e->getMessage(),
                'code' => $e->getCode(),
                'content' => $content,
            ]);
            throw $e;
        }
        $this->activitypubLogger->debug('response', [
            'content' => $content,
            'code' => $response->getStatusCode(),
        ]);
    }

    private function generateDigest(string $body): string
    {
        return base64_encode(hash('sha256', $body, true));
    }

    private function generateSignature(User $user, string $inboxUrl, string $date, string $digest, string $method = 'post'): string
    {
        if ($user->getPrivateKey() === null) {
            throw new RuntimeException();
        }
        $urlParts = parse_url($inboxUrl);
        if (!is_array($urlParts)) {
            throw new RuntimeException();
        }
        if (!array_key_exists('host', $urlParts) || !array_key_exists('path', $urlParts)) {
            throw new RuntimeException();
        }
        $host = $urlParts['host'];
        $path = $urlParts['path'];
        if (array_key_exists('query', $urlParts)) {
            $query = $urlParts['query'];
            if (trim($query) !== '') {
                $path .= '?'.$query;
            }
        }
        $signed_string = sprintf("(request-target): %s %s\nhost: %s\ndate: %s\ndigest: SHA-256=%s", $method, $path, $host, $date, $digest);
        openssl_sign($signed_string, $signature, $user->getPrivateKey(), OPENSSL_ALGO_SHA256);
        $signature = base64_encode($signature); // phpcs:ignore
        $key_id = $user->getProfileUrl().'#main-key';

        return sprintf('keyId="%s",algorithm="rsa-sha256",headers="(request-target) host date digest",signature="%s"', $key_id, $signature);
    }

    /**
     * @param  string  $webfingerUrl
     * @return array<string, mixed>
     * @throws ClientExceptionInterface
     * @throws JsonException
     * @throws RedirectionExceptionInterface
     * @throws ServerExceptionInterface
     * @throws TransportExceptionInterface
     */
    public function webfinger(string $webfingerUrl): array
    {
        $webfingerResult = $this->httpClient->request('GET', $webfingerUrl, [
            'headers' => [
                'Accept' => 'application/json',
            ],
        ]);
        $content = json_decode($webfingerResult->getContent(), true, 512, JSON_THROW_ON_ERROR);
        if (is_array($content)) {
            return $content;
        }

        return [];
    }

    /**
     * @return array<string, mixed>
     * @throws ClientExceptionInterface
     * @throws JsonException
     * @throws RedirectionExceptionInterface
     * @throws ServerExceptionInterface
     * @throws TransportExceptionInterface
     */
    public function load(string $url, ?User $user = null): array
    {
        $headers = [
            'Accept' => 'application/activity+json,application/ld+json,application/json',
        ];

        if ($user !== null) {
            $date = gmdate('D, d M Y H:i:s T');
            $digest = $this->generateDigest('');
            $signature = $this->generateSignature($user, $url, $date, $digest, 'get');

            $headers['Digest'] = 'SHA-256='.$digest;
            $headers['Signature'] = $signature;
            $headers['Date'] = $date;
        }

        $result = $this->httpClient->request('GET', $url, [
            'headers' => $headers,
        ]);
        $content = json_decode($result->getContent(), true, 512, JSON_THROW_ON_ERROR);
        if (is_array($content)) {
            return $content;
        }

        return [];
    }
}

https://gist.github.com/lostfocus/a6202e2aa8cd8073e686b2c97b955595#file-client-php-L151 should be:

'Accept' => 'application/jrd+json,application/json',