Resolves podcast guids to feed urls.
This is a podcast guid resolver. It takes a CSV file of guids and feed urls and loads them in a hashmap. When a GET
request is sent, it's host header is parsed to find the first part. That substring is then used as the key lookup
on the hashmap. If a url value is found for that key, it is returned as a plain/text HTTP response body.
Send a GET to:
917393e3-1b1e-5cef-ace4-edaa54e1f810.guid.podcastindex.org
...and get back: