This hook can be implemented to return a proxy to try when
connecting to URL. Returned proxies are tried in the order in
which they are returned by the multifile hook try_proxy/4.
Pre-defined proxy methods are:
- connect directly to the resource
- proxy(Host, Port)
- Connect to the resource using an HTTP proxy. If the
resource is not an HTTP URL, then try to connect using the
CONNECT verb, otherwise, use the GET verb.
- socks(Host, Port)
- Connect to the resource via a SOCKS5 proxy
These correspond to the proxy methods defined by PAC Proxy
Additional methods can be returned if suitable clauses for
http:http_connection_over_proxy/6 or try_proxy/4 are defined.