Add Secret Scanning validation sample in JavaScript

Author: Piccirello

content/developers/overview/secret-scanning.md

@@ -278,6 +278,48 @@ openssl_key = OpenSSL::PKey::EC.new(current_key)
 puts openssl_key.verify(OpenSSL::Digest::SHA256.new, Base64.decode64(signature), payload.chomp)
 ```
 
+**Validation sample in JavaScript**
+```js
+const crypto = require("crypto");
+const axios = require("axios");
+
+const GITHUB_KEYS_URI = "https://api.github.com/meta/public_keys/secret_scanning";
+
+/**
+ * Verify a payload and signature against a public key
+ * @param {String} payload the value to verify
+ * @param {String} signature the expected value
+ * @param {String} keyID the id of the key used to generated the signature
+ * @return {void} throws if the signature is invalid
+ */
+const verify_signature = async (payload, signature, keyID) => {
+  if (typeof payload !== "string" || payload.length === 0) {
+    throw new Error("Invalid payload");
+  }
+  if (typeof signature !== "string" || signature.length === 0) {
+    throw new Error("Invalid signature");
+  }
+  if (typeof keyID !== "string" || keyID.length === 0) {
+    throw new Error("Invalid keyID");
+  }
+
+  const keys = (await axios.get(GITHUB_KEYS_URI)).data;
+  if (!(keys?.public_keys instanceof Array) || keys.length === 0) {
+    throw new Error("No public keys found");
+  }
+
+  const publicKey = keys.public_keys.find((k) => k.key_identifier === keyID) ?? null;
+  if (publicKey === null) {
+    throw new Error("No public key found matching key identifier");
+  }
+
+  const verify = crypto.createVerify("SHA256").update(payload);
+  if (!verify.verify(publicKey.key, Buffer.from(signature, "base64"), "base64")) {
+    throw new Error("Signature does not match payload");
+  }
+};
+```
+
 #### Implement secret revocation and user notification in your secret alert service
 
 For {% data variables.product.prodname_secret_scanning %} in public repositories, you can enhance your secret alert service to revoke the exposed secrets and notify the affected users. How you implement this in your secret alert service is up to you, but we recommend considering any secrets that {% data variables.product.prodname_dotcom %} sends you messages about as public and compromised.