Integration: Webhook receiver with HMAC SHA-256 signature validation (#2386)

* Create README.md

* Create HmacUtils.js

* Create WebhookHmacReceiver.js

Author: franks883

Integration/Scripted REST Api/Webhook receiver with HMAC SHA-256 validation/HmacUtils.js

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+// Script Include: HmacUtils
+// Purpose: Compute HMAC SHA-256 and constant-time compare.
+
+var HmacUtils = Class.create();
+HmacUtils.prototype = {
+  initialize: function() {},
+
+  hmacSha256Hex: function(secret, message) {
+    var mac = Packages.javax.crypto.Mac.getInstance('HmacSHA256');
+    var key = new Packages.javax.crypto.spec.SecretKeySpec(
+      new Packages.java.lang.String(secret).getBytes('UTF-8'),
+      'HmacSHA256'
+    );
+    mac.init(key);
+    var raw = mac.doFinal(new Packages.java.lang.String(message).getBytes('UTF-8'));
+
+    var sb = new Packages.java.lang.StringBuilder();
+    for (var i = 0; i < raw.length; i++) {
+      var hex = Packages.java.lang.Integer.toHexString((raw[i] & 0xff) | 0x100).substring(1);
+      sb.append(hex);
+    }
+    return sb.toString();
+  },
+
+  constantTimeEquals: function(a, b) {
+    var A = String(a || '');
+    var B = String(b || '');
+    if (A.length !== B.length) return false;
+    var diff = 0;
+    for (var i = 0; i < A.length; i++) diff |= A.charCodeAt(i) ^ B.charCodeAt(i);
+    return diff === 0;
+  },
+
+  type: 'HmacUtils'
+};

Integration/Scripted REST Api/Webhook receiver with HMAC SHA-256 validation/README.md

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+# Webhook receiver with HMAC SHA-256 validation
+
+## What this solves
+Inbound webhooks should be verified to ensure the payload really came from the sender. This receiver validates an `X-Signature` header containing an HMAC SHA-256 of the request body using a shared secret. Invalid signatures return HTTP 401.
+
+## Where to use
+- Scripted REST API resource script
+- Include the `HmacUtils` Script Include in the same app or global
+
+## How it works
+- Reads raw request body and the `X-Signature` header
+- Computes HMAC SHA-256 using the shared secret
+- Compares in constant time to avoid timing attacks
+- If valid, inserts the payload into a target table or queues it for processing
+
+## Configure
+- Set `SHARED_SECRET` (prefer credentials or encrypted properties)
+- Update `TARGET_TABLE` for successful inserts
+
+## References
+- Scripted REST APIs  
+  https://www.servicenow.com/docs/bundle/zurich-application-development/page/build/applications/task/create-scripted-rest-api.html
+- REST API request/response objects  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideHTTPRequest/concept/c_scripted-rest-api-request.html
+- Java crypto (used server-side)  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/Script/server_apis/concept/java-use.html

Integration/Scripted REST Api/Webhook receiver with HMAC SHA-256 validation/WebhookHmacReceiver.js

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+// Scripted REST API Resource Script: Webhook receiver with HMAC validation
+(function process(/*RESTAPIRequest*/ request, /*RESTAPIResponse*/ response) {
+  var SHARED_SECRET = gs.getProperty('x_acme.webhook.secret', '');
+  var TARGET_TABLE = 'x_acme_inbound_webhook'; // replace with your table
+
+  try {
+    var body = request.body && request.body.data ? request.body.data : '';
+    var signature = request.getHeader('X-Signature') || ''; // hex HMAC hash
+
+    if (!SHARED_SECRET) {
+      response.setStatus(500);
+      response.setBody({ error: 'Server not configured' });
+      return;
+    }
+    if (!signature || !body) {
+      response.setStatus(400);
+      response.setBody({ error: 'Missing signature or body' });
+      return;
+    }
+
+    var util = new HmacUtils();
+    var expected = util.hmacSha256Hex(SHARED_SECRET, body);
+
+    if (!util.constantTimeEquals(expected, signature)) {
+      response.setStatus(401);
+      response.setBody({ error: 'Invalid signature' });
+      return;
+    }
+
+    // Valid payload: insert a record for processing
+    var rec = new GlideRecord(TARGET_TABLE);
+    rec.initialize();
+    rec.payload = body;
+    rec.signature = signature;
+    rec.insert();
+
+    response.setStatus(200);
+    response.setBody({ ok: true });
+  } catch (e) {
+    response.setStatus(500);
+    response.setBody({ error: String(e) });
+  }
+})(request, response);