Register Goal for expanding the HTTP request handler. Goal is called
as below. If Goal fail the request is passed to the next expansion
unmodified.
call(Goal, Request0, Request, Options)
If multiple goals are registered they expand the request in a
pipeline starting with the expansion hook with the lowest rank.
Besides rewriting the request, for example by validating the user
identity based on HTTP authentication or cookies and adding this to
the request, the hook may raise HTTP exceptions to indicate a bad
request, permission error, etc. See http_status_reply/4.
Initially, auth_expansion/3 is registered with rank 100 to deal
with the older http:authenticate/3 hook.
