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When Schedo sends a webhook, it includes a signature in the x-schedo-signature header. This signature allows you to verify that the request really came from Schedo and not from a malicious third party.

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Why Verify the Signature?

Anyone can send a POST request to your webhook URL. By verifying the signature, you ensure that only requests genuinely sent by Schedo (using your secret) are accepted and processed.

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How the Signature is Generated

  1. Schedo takes the raw request body (the JSON payload).
  2. Schedo computes an HMAC-SHA256 hash of this payload, using your unique signing secret as the key.
  3. Schedo sends the resulting hash (as a hex string) in the x-schedo-signature header.

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How to Verify the Signature

To verify the request:
  1. Read the raw request body (exactly as received).
  2. Compute your own HMAC-SHA256 hash of the body, using your signing secret.
  3. Compare your computed hash to the value in the x-schedo-signature header.
  4. If they match, the request is authentic.

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Example: Manual Signature Verification in TypeScript/Node.js

import { createHmac, timingSafeEqual } from "crypto";
import { NextRequest, NextResponse } from "next/server";

// Your secret from Schedo settings (keep this safe!)
const SCHEDO_SIGNING_SECRET = process.env.SCHEDO_SIGNING_SECRET!;

function computeSignature(payload: Buffer | string, secret: string): string {
  return createHmac("sha256", secret).update(payload).digest("hex");
}

function isValidSignature(payload: Buffer | string, signature: string, secret: string): boolean {
  const expected = computeSignature(payload, secret);
  // Use timingSafeEqual to prevent timing attacks
  try {
    return timingSafeEqual(Buffer.from(signature, "hex"), Buffer.from(expected, "hex"));
  } catch {
    return false;
  }
}

export async function POST(req: NextRequest) {
  // Read the raw body as a Buffer
  const body = await req.text();
  const signature = req.headers.get("x-schedo-signature") ?? "";

  if (!isValidSignature(body, signature, SCHEDO_SIGNING_SECRET)) {
    return NextResponse.json({ error: "Invalid signature" }, { status: 400 });
  }

  // If you get here, the request is authentic!
  const data = JSON.parse(body);
  // ... handle your logic

  return NextResponse.json({ success: true });
}

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Key Points

  • Always use the raw body (not a parsed object) for signature calculation.
  • Use timingSafeEqual for comparison to prevent timing attacks.
  • Never share your signing secret.
By following these steps, you can ensure that only trusted requests from Schedo are processed by your webhook endpoint.
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