Feat: Add Webhook Signature Verification

README.md

@@ -57,6 +57,7 @@ If you or your business relies on this package, it's important to support the de
 - [Meta Information](#meta-information)
 - [Troubleshooting](#troubleshooting)
 - [Testing](#testing)
+- [Webhooks][#webhooks]
 - [Services](#services)
   - [Azure](#azure)
 
@@ -3114,6 +3115,25 @@ $completion = $client->completions()->create([
 ]);
 ```
 
+## Webhooks
+
+The package includes a signature verifier for OpenAI webhooks. To verify the signature of incoming webhook requests, you can use the `OpenAI\Webhooks\SignatureVerifier` class.
+
+```php
+use OpenAI\Webhooks\SignatureVerifier;
+use OpenAI\Exceptions\WebhookVerificationException;
+
+$verifier = new SignatureVerifier('whsec_{your-webhook-signing-secret}');
+
+try {
+    $verifier->verify($incomingRequest);
+
+    // The request is verified
+} catch (WebhookVerificationException $exception) {
+    // The request could not be verified
+}
+```
+
 ## Services
 
 ### Azure

src/Enums/Webhooks/WebhookEvent.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace OpenAI\Enums\Webhooks;
+
+enum WebhookEvent: string
+{
+    case BatchCancelled = 'batch.cancelled';
+    case BatchCompleted = 'batch.completed';
+    case BatchExpired = 'batch.expired';
+    case BatchFailed = 'batch.failed';
+    case EvalRunCancelled = 'eval.run.canceled';
+    case EvalRunFailed = 'eval.run.failed';
+    case EvalRunSucceeded = 'eval.run.succeeded';
+    case FineTuningJobCancelled = 'fine_tuning.job.cancelled';
+    case FineTuningJobFailed = 'fine_tuning.job.failed';
+    case FineTuningJobSucceeded = 'fine_tuning.job.succeeded';
+    case RealtimeCallIncoming = 'realtime.call.incoming';
+    case ResponseCancelled = 'response.cancelled';
+    case ResponseCompleted = 'response.completed';
+    case ResponseFailed = 'response.failed';
+    case ResponseIncomplete = 'response.incomplete';
+    case VideoCompleted = 'video.completed';
+    case VideoFailed = 'video.failed';
+}

src/Exceptions/WebhookVerificationException.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace OpenAI\Exceptions;
+
+use RuntimeException;
+
+class WebhookVerificationException extends RuntimeException
+{
+    protected function __construct(string $message, int $code = 0)
+    {
+        parent::__construct('Failed to verify webhook: '.$message, $code);
+    }
+
+    public static function missingRequiredHeader(): self
+    {
+        return new self('Missing required header', 100);
+    }
+
+    public static function noMatchingSignature(): self
+    {
+        return new self('No matching signature found', 200);
+    }
+
+    public static function invalidTimestamp(): self
+    {
+        return new self('Invalid timestamp', 300);
+    }
+
+    public static function timestampMismatch(): self
+    {
+        return new self('Message timestamp outside tolerance window', 301);
+    }
+}

src/Webhooks/WebhookSignatureVerifier.php

@@ -0,0 +1,124 @@
+<?php
+
+namespace OpenAI\Webhooks;
+
+use DateTimeInterface;
+use OpenAI\Exceptions\WebhookVerificationException;
+use Psr\Http\Message\RequestInterface;
+use RuntimeException;
+use UnexpectedValueException;
+
+readonly class WebhookSignatureVerifier
+{
+    private string $secret;
+
+    /**
+     * @throws UnexpectedValueException
+     */
+    public function __construct(
+        string $secret,
+        private int $tolerance = 300,
+        string $secretPrefix = 'whsec_',
+    ) {
+        if (str_starts_with($secret, $secretPrefix)) {
+            $secret = substr($secret, strlen($secretPrefix));
+        }
+
+        $this->secret = base64_decode($secret, true)
+            ?: throw new UnexpectedValueException('Invalid secret format');
+    }
+
+    /**
+     * @throws WebhookVerificationException|RuntimeException
+     */
+    public function verify(RequestInterface $request): void
+    {
+        $body = $request->getBody();
+        $payload = $body->getContents();
+        $body->rewind();
+
+        $this->verifySignature($payload, [
+            'webhook-id' => trim($request->getHeaderLine('webhook-id')) ?: null,
+            'webhook-timestamp' => trim($request->getHeaderLine('webhook-timestamp')) ?: null,
+            'webhook-signature' => trim($request->getHeaderLine('webhook-signature')) ?: null,
+        ]);
+    }
+
+    /**
+     * @param  array{webhook-id: ?non-falsy-string, webhook-timestamp: ?non-falsy-string, webhook-signature: ?non-falsy-string}  $headers
+     *
+     * @throws WebhookVerificationException
+     */
+    final protected function verifySignature(string $payload, array $headers): void
+    {
+        if (! isset($headers['webhook-id'], $headers['webhook-timestamp'], $headers['webhook-signature'])) {
+            throw WebhookVerificationException::missingRequiredHeader();
+        }
+
+        [
+            'webhook-id' => $messageId,
+            'webhook-timestamp' => $messageTimestamp,
+            'webhook-signature' => $messageSignature,
+        ] = $headers;
+        $timestamp = $this->verifyTimestamp($messageTimestamp);
+        $signature = $this->sign($messageId, $timestamp, $payload);
+        [, $expectedSignature] = explode(',', $signature, 2);
+        $passedSignatures = explode(' ', $messageSignature);
+
+        foreach ($passedSignatures as $versionedSignature) {
+            [$version, $passedSignature] = explode(',', $versionedSignature, 2);
+
+            if (strcmp($version, 'v1') !== 0) {
+                continue;
+            }
+
+            if (hash_equals($expectedSignature, $passedSignature)) {
+                return;
+            }
+        }
+
+        throw WebhookVerificationException::noMatchingSignature();
+    }
+
+    /**
+     * @throws WebhookVerificationException
+     *
+     * @internal
+     */
+    final public function sign(string $messageId, DateTimeInterface|int $timestamp, string $payload): string
+    {
+        $timestamp = match (true) {
+            $timestamp instanceof DateTimeInterface => $timestamp->getTimestamp(),
+            is_int($timestamp) && $timestamp > 0 => $timestamp,
+            default => throw WebhookVerificationException::invalidTimestamp(),
+        };
+
+        $hash = hash_hmac(
+            'sha256',
+            implode('.', [$messageId, $timestamp, $payload]),
+            $this->secret,
+        );
+        $signature = base64_encode(pack('H*', $hash));
+
+        return 'v1,'.$signature;
+    }
+
+    /**
+     * @throws WebhookVerificationException
+     */
+    protected function verifyTimestamp(string $timestampHeader): int
+    {
+        $now = time();
+        $timestamp = (int) $timestampHeader;
+
+        if ($timestamp < ($now - $this->tolerance)) {
+            throw WebhookVerificationException::timestampMismatch();
+        }
+
+        if ($timestamp > ($now + $this->tolerance)) {
+            throw WebhookVerificationException::timestampMismatch();
+        }
+
+        return $timestamp;
+    }
+}