fix(events,github): fixes signature validation by using raw req body

Adds raw body information (body as buffer, encoding)
to `RequestDetails` to support more request validation
use cases.

Additionally, uses the raw body to retrieve the transmitted
JSON string unparsed/raw to correctly validate the signature.

Previously, we re-stringified the parsed JSON payload
which could lead to different JSON strings.
Those differences can lead to the rejection of requests
due to a mismatch in expected signature.

Fixes: #26709
Relates-to: PR #26884
Co-authored-by: Christopher Diaz <cdiaz@rvohealth.com>
Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

plugins/events-node/report.api.md

@@ -3,6 +3,8 @@
 > Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
 
 ```ts
+/// <reference types="node" />
+
 import { AuthService } from '@backstage/backend-plugin-api';
 import { DiscoveryService } from '@backstage/backend-plugin-api';
 import { LifecycleService } from '@backstage/backend-plugin-api';
@@ -114,10 +116,14 @@ export interface HttpPostIngressOptions {
   validator?: RequestValidator;
 }
 
-// @public (undocumented)
+// @public
 export interface RequestDetails {
   body: unknown;
   headers: Record<string, string | string[] | undefined>;
+  raw: {
+    body: Buffer;
+    encoding: BufferEncoding;
+  };
 }
 
 // @public

plugins/events-node/src/api/http/validation/RequestDetails.ts

@@ -15,6 +15,8 @@
  */
 
 /**
+ * View on an incoming request that has to be validated.
+ *
  * @public
  */
 export interface RequestDetails {
@@ -26,4 +28,18 @@ export interface RequestDetails {
    * Key-value pairs of header names and values. Header names are lower-cased.
    */
   headers: Record<string, string | string[] | undefined>;
+  /**
+   * Raw request details.
+   */
+  raw: {
+    /**
+     * Raw request body (buffer).
+     */
+    body: Buffer;
+    /**
+     * Encoding of the raw request body.
+     * Can be used to decode the raw request body like `raw.body.toString(raw.encoding)`.
+     */
+    encoding: BufferEncoding;
+  };
 }