feat: capture raw body bytes for v4 hmac calculation

TICKET: CAAS-659

Author: MohammedRyaan786

modules/express/src/clientRoutes.ts

@@ -1192,6 +1192,38 @@ async function handleNetworkV1EnterpriseClientConnections(
   return handleProxyReq(req, res, next);
 }
 
+/**
+ * Helper to send request body, using raw bytes when available.
+ *
+ * For v4 HMAC authentication, we need to send the exact bytes that were
+ * received from the client to ensure the HMAC signature matches.
+ * The rawBodyBuffer is captured by body-parser's verify callback before
+ * JSON parsing, preserving exact whitespace, key ordering, etc.
+ *
+ * For v2/v3, sending the raw string also works because serializeRequestData
+ * now properly returns strings as-is for HMAC calculation.
+ *
+ * @param request - The superagent request object
+ * @param req - The Express request containing body and rawBodyBuffer
+ * @returns The request with body attached
+ */
+function sendRequestBody(request: ReturnType<BitGo['post']>, req: express.Request) {
+  if (req.rawBodyBuffer) {
+    // Preserve original Content-Type header from client
+    const contentTypeHeader = req.headers['content-type'];
+    if (contentTypeHeader) {
+      request.set('Content-Type', Array.isArray(contentTypeHeader) ? contentTypeHeader[0] : contentTypeHeader);
+    }
+    // Send raw body as UTF-8 string to preserve exact bytes for HMAC.
+    // JSON is always UTF-8 (RFC 8259), so this is lossless for JSON bodies.
+    // serializeRequestData will return this string as-is for HMAC calculation.
+    return request.send(req.rawBodyBuffer.toString('utf8'));
+  }
+
+  // Fall back to parsed body for backward compatibility (e.g., non-JSON bodies)
+  return request.send(req.body);
+}
+
 /**
  * Redirect a request using the bitgo request functions.
  * @param bitgo
@@ -1214,19 +1246,19 @@ export function redirectRequest(
       request = bitgo.get(url);
       break;
     case 'POST':
-      request = bitgo.post(url).send(req.body);
+      request = sendRequestBody(bitgo.post(url), req);
       break;
     case 'PUT':
-      request = bitgo.put(url).send(req.body);
+      request = sendRequestBody(bitgo.put(url), req);
       break;
     case 'PATCH':
-      request = bitgo.patch(url).send(req.body);
+      request = sendRequestBody(bitgo.patch(url), req);
       break;
     case 'OPTIONS':
-      request = bitgo.options(url).send(req.body);
+      request = sendRequestBody(bitgo.options(url), req);
       break;
     case 'DELETE':
-      request = bitgo.del(url).send(req.body);
+      request = sendRequestBody(bitgo.del(url), req);
       break;
   }
 
@@ -1267,7 +1299,12 @@ function apiResponse(status: number, result: any, message?: string): ApiResponse
   return new ApiResponseError(message, status, result);
 }
 
-const expressJSONParser = bodyParser.json({ limit: '20mb' });
+const expressJSONParser = bodyParser.json({
+  limit: '20mb',
+  verify: (req, res, buf) => {
+    (req as express.Request).rawBodyBuffer = buf;
+  },
+});
 
 /**
  * Perform body parsing here only on routes we want

modules/express/src/expressApp.ts

@@ -302,7 +302,18 @@ export function app(cfg: Config): express.Application {
   checkPreconditions(cfg);
   debug('preconditions satisfied');
 
-  app.use(bodyParser.json({ limit: '20mb' }));
+  app.use(
+    bodyParser.json({
+      limit: '20mb',
+      verify: (req, res, buf) => {
+        // Store the raw body buffer on the request object.
+        // This preserves the exact bytes before JSON parsing,
+        // which may alter whitespace, key ordering, etc.
+        // Required for v4 HMAC authentication.
+        (req as express.Request).rawBodyBuffer = buf;
+      },
+    })
+  );
 
   // Be more robust about accepting URLs with double slashes
   app.use(function replaceUrlSlashes(req, res, next) {