A reverse proxy for golang that allows requests to be blocked/aborted before being sent upstream.
The Director function, unlike the ReverseProxy in the httputil package,
returns a bool that determines whether a Request should be sent to the
upstream server or not. If false is returned, by default, a 403 response
will be returned. This can be customized via the CreateResponse function.
Otherwise, the ConditionalReverseProxy behaves exactly the same way as the
ReverseProxy from httputil.
Requires Go 1.13+.