Issue Summary

API requests that result in 4xx error codes (such as 429 and  400) are missing the access-control-allow-origin and other access-control-allow-* headers, preventing the power-up from accessing the retry-after and x-rate-limit-* headers.

This issue happens on multiple API endpoints, but I'm sharing the *https://api.trello.com/1/batch/* endpoint for reference.

Steps to Reproduce

1. Perform an API request to https://api.trello.com/1/batch/* endpoint that reaches the API rate limit and returns a *429 status code.

Expected Results

The access-control-allow-* headers are available on the request, allowing the requester to access the response headers.

Actual Results

The access-control-allow-* headers are not available on the request.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available