debug: add SigV4 mismatch logging with expected vs received signature

src/utils/s3/auth.ts

@@ -331,7 +331,22 @@ export const verifySignature = async (
   const signingKey = await getSigningKey(s3SecretKey, dateStamp, region);
   const expectedSignature = await hmacHex(signingKey, stringToSign);
 
+  // TEMP DEBUG: log signature mismatch details
   if (!timingSafeCompare(expectedSignature, parsed.signature)) {
+    const debugInfo = {
+      method,
+      uri: canonicalUri,
+      canReq: canonicalRequest.slice(0, 400),
+      hashedCR: hashedCanonicalRequest,
+      amzDate,
+      dateStamp,
+      scope: credentialScope,
+      stringToSign: stringToSign.slice(0, 300),
+      expectedSig: expectedSignature,
+      receivedSig: parsed.signature,
+      accessKey: parsed.accessKey,
+    };
+    console.error('SIGV4_MISMATCH:' + JSON.stringify(debugInfo));
     return { isValid: false, credential: null, errorCode: 'SignatureDoesNotMatch' };
   }