Given any URL, will return a stream to that URL using the HTTP client and GET method
for the authentication as defined in this content source's configuration.
Parses the simple index txt file whose format is simply "location|sha256" where location
is a relative filepath where the file is found on the content source.
This is a basic implementation of a content source that provides primative package
synchronization with a URL-based content source, such as an HTTP server.