III.d Controlling Remote Access
-------------------------------
On occasion one may have a need to restrict access to certain documents offered
by your server.  For example, licensed or sensitive information, or access to
resources paid for by a certain community which are to be accessed only by the
authorized or paying customers of that resource.  Access may be controlled at
the global level using one or more Access: specifications in the server
configuration file.  Finer granularity may be achieved by using one or more
Access= specifications at the top of any .LINKS files, or even finer by
specifying one or more Access= specifications within individual link tuples or
in lookasides, either traditional lookaside files or ACL-resident lookasides.

An example taken from a live site using these facilities to control access
follows:

	Name=UnCover Periodical Search and Delivery Service
	Type=8
	Port=23
	Numb=5
	Access=default !browse,!read,!search
	Access=.unc.edu browse
	Access=.duke.edu browse
	Access=.ncsu.edu browse
	Access=152.1. browse
	Access=152.2. browse
	Access=152.3. browse
	Path=
	Host=uncover.lib.ncsu.edu

This example limits access to the telnet service "Uncover..." to no users
except those whose hosts match the specified host names.  Notice both the DNS
names and the dotted decimal addresses are specified to allow a wide range of
hosts within these domains.  The link tuple will not even be offered to hosts
which don't satisfy the access filter.

Another example from the same site, which prevents the directory from even
being offered on a menu to a non-local site:

	Name=TRLN Private Gopherhole
	Type=1
	Port=+
	Access=default !b,!r,!s
	Access=trln.lib.unc.edu b,r,s
	Numb=12
	Path=1gopher_root:[other_services.trln_private]
	Host=+

This example allows only the host site's clients to access the directory in
question.  That directory then also contains a .LINKS file, which is also
access controlled, even if the client knows how to specify it in a way which
allows bypassing of the access-controlled pointer, above:

	DName=%fn [%ts, %sz]
	Ignore=.doc
	Ignore=.dir
	Ignore=.txt
	Ignore=.dia
	Ignore=.lis
	Access=default !b,!r,!s
	Access=trln.lib.unc.edu b,r,s

	Name=About TRLN Private
	Type=0
	Port=+
	Numb=1
	Path=0gopher_root:[other_services.trln_private]_about.txt
	Host=+

The Access: specifications in the configuration file, and the Access=
specifications which can be found in .LINKS files, in link tuples and in
lookasides are semantically the same, and virtually the same in syntax as well
-- the only difference is the use of ":" in the configuration file syntax, and
"=" in the .LINKS, link tuple and lookaside syntax.

.