> For the complete documentation index, see [llms.txt](https://docs.partssource.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.partssource.com/webhooks/verifying-deliveries.md).

# Verifying Deliveries

The normative signature specification and reference implementations

## The signature specification

**Signed content:** `<X-PS-Timestamp value>.<raw request body bytes>`

**Algorithm:** HMAC-SHA256, hex-encoded; key = your endpoint secret

**Reject if:** the timestamp is more than 300 seconds from now, or the signature differs (compare in constant time)

**Common failure:** verifying against a re-parsed or re-serialized body. Verify the exact bytes received, before any JSON parsing.

## Reference implementations

{% tabs %}
{% tab title="Node" %}

```javascript
const express = require('express');
const crypto = require('crypto');
const app = express();

app.post('/webhooks/partssource',
  // Keep the raw bytes. Do not use express.json() on this route:
  // the signature covers the body exactly as sent.
  express.raw({ type: 'application/json' }),
  (req, res) => {
    const signature = req.headers['x-ps-signature'] ?? '';
    const timestamp = req.headers['x-ps-timestamp'] ?? '';

    // Reject deliveries older than five minutes (replay protection).
    if (Math.abs(Date.now() / 1000 - Number(timestamp)) > 300) {
      return res.status(401).end();
    }

    // Verify HMAC-SHA256 over "<timestamp>.<raw body>" in constant time.
    const expected = crypto
      .createHmac('sha256', process.env.PS_WEBHOOK_SECRET)
      .update(`${timestamp}.${req.body}`)
      .digest('hex');
    const a = Buffer.from(signature);
    const b = Buffer.from(expected);
    if (a.length !== b.length || !crypto.timingSafeEqual(a, b)) {
      return res.status(401).end();
    }

    // Acknowledge immediately; process asynchronously.
    res.status(200).end();
    queue.push(JSON.parse(req.body));
  });
```

{% endtab %}

{% tab title="C#" %}

```csharp
app.MapPost("/webhooks/partssource", async (HttpRequest req) =>
{
    using var reader = new StreamReader(req.Body);
    var body = await reader.ReadToEndAsync(); // raw body, before any model binding

    var signature = req.Headers["X-PS-Signature"].ToString();
    var timestamp = req.Headers["X-PS-Timestamp"].ToString();

    if (!long.TryParse(timestamp, out var ts) ||
        Math.Abs(DateTimeOffset.UtcNow.ToUnixTimeSeconds() - ts) > 300)
        return Results.Unauthorized();

    var secret = Environment.GetEnvironmentVariable("PS_WEBHOOK_SECRET")!;
    using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
    var expected = Convert.ToHexString(
        hmac.ComputeHash(Encoding.UTF8.GetBytes($"{timestamp}.{body}"))).ToLowerInvariant();

    if (!CryptographicOperations.FixedTimeEquals(
            Encoding.UTF8.GetBytes(expected), Encoding.UTF8.GetBytes(signature)))
        return Results.Unauthorized();

    await queue.EnqueueAsync(body); // process asynchronously
    return Results.Ok();
});
```

{% endtab %}

{% tab title="Python" %}

```python
@app.post("/webhooks/partssource")
def webhook():
    raw = request.get_data()  # raw bytes, before any JSON parsing
    signature = request.headers.get("X-PS-Signature", "")
    timestamp = request.headers.get("X-PS-Timestamp", "0")

    if abs(time.time() - float(timestamp)) > 300:
        abort(401)

    expected = hmac.new(
        os.environ["PS_WEBHOOK_SECRET"].encode(),
        f"{timestamp}.".encode() + raw,
        hashlib.sha256,
    ).hexdigest()

    if not hmac.compare_digest(expected, signature):
        abort(401)

    queue.enqueue(raw)  # process asynchronously
    return "", 200
```

{% endtab %}
{% endtabs %}

{% hint style="info" %}
Every other page links here rather than restating this specification. If a sample and this specification ever disagree, the specification wins.
{% endhint %}


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