Is there any way to login with worker credentials inside the web page using a Web Browser? It's all http protocol and I shuold get some JSON response if I understand.
Well, you need to send a POST request with the appropriate JSON-RPC method call to get a JSON response. But you can still point your browser at the proxy (just remove "/admin/..." from the URL) and authenticate as a worker. If you successfully authenticate, you'll get back a 400 Bad Request ("I don't understand what you said") response.