fix signature verification of camelCased subresource URIs

Author: kherock

Diff for: lib/middleware/authentication.js

@@ -55,9 +55,8 @@ module.exports = () =>
       return next();
     }
 
-    const query = mapKeys(ctx.query, (value, key) => key.toLowerCase());
     const amzQueryHeaders = pickBy(
-      query,
+      mapKeys(ctx.query, (value, key) => key.toLowerCase()),
       (value, key) =>
         key.startsWith('x-amz-') &&
         // x-amz-website-redirect-location isn't a canonical header
@@ -108,7 +107,7 @@ module.exports = () =>
       .map(encodeURIComponentRFC3986)
       .join('/');
 
-    const canonicalizedQueryString = Object.entries(query)
+    const canonicalizedQueryString = Object.entries(ctx.query)
       .filter(
         ([param]) =>
           SUBRESOURCES[param] ||