NAME

       dacs_uproxy - minimal HTTP proxying

SYNOPSIS

       dacs_uproxy [dacsoptions[1]]

DESCRIPTION

       This web service is part of the DACS suite.

       The dacs_uproxy web service accepts an incoming HTTP request (the initial request), then
       reissues a nearly identical HTTP request to a different URL (the proxied request) and
       returns its unaltered response. The initial request must use either the GET or POST HTTP
       method; the proxied request will use the same method as the initial request. Note that the
       origin server (the web server that receives the proxied request) will see a request that
       originates at the host that runs dacs_uproxy, not the host that issues the initial
       request.

       When run on a firewall host, the program can be useful for forwarding incoming requests to
       interior hosts. An origin server does not need to be running DACS. All access control is
       performed by the jurisdiction that runs dacs_uproxy. Similarly, the program can be useful
       for forwarding requests that originate behind the firewall, subject to access control
       permission.

       dacs_uproxy is not a transparent proxy server. A request URL must be explicitly addressed
       to it and include a (partial) name for the target resource.

           Security
           The program must be configured with care because it can expose otherwise inaccessible
           hosts to arbitrary HTTP requests from any source that can connect to dacs_uproxy.

           Particular care must be taken if a program that is invoked by dacs_uproxy generates a
           redirect that may be handled internally by the program's web server. In this event the
           new request arising from the redirection will not automatically be subjected to access
           control because the new request does come through dacs_uproxy. Therefore, local
           redirects must be avoided by proxied web services, resources that might be invoked
           through a local redirect must be publicly accessible, or authorization checking must
           somehow be arranged for these resources.

           Access control rules are primarily responsible for expressing restrictions on what can
           be proxied and who can use this service. By default, all access to this service is
           denied. Additionally, UPROXY_APPROVED[2] directives must be configured to allow
           proxying to specific origin servers.

           Although in its current form the program has the effect of anonymizing the proxied
           request, this is more of a bug than a feature. Future versions may forward an initial
           request's headers and other information.

       With the exception of the Cookie header, most request headers that accompany the initial
       request are sent with the proxied request.  dacs_uproxy makes no attempt to "impersonate"
       the user's host, however. Therefore, to the origin server it appears as if the request is
       coming from dacs_uproxy and the IP address from which the forwarded request is sent. Any
       cookies sent with the initial request are interpreted by dacs_uproxy (e.g., to identify
       the user making the request for access control purposes). At present, it is not possible
       to forward cookies with the proxied request.

       So that the proxied web service can tell that it is being invoked by dacs_uproxy, an
       extension header named DACS-Uproxy-Via is included with the forwarded request. Its value
       is the URL of dacs_uproxy with the proxied host appended. With Apache, its value can be
       accessed from the environment variable HTTP_DACS_UPROXY_VIA.

       If dacs_uproxy is passed a DACS_APPROVAL[3] value, that value is forwarded with the
       request through the DACS-Uproxy-Approval header and made available by Apache in the
       HTTP_DACS_UPROXY_APPROVAL environment variable. A program invoked indirectly through
       dacs_uproxy can use this information to confirm that DACS authorized the request.

       If the forwarded request generates a redirect (a 3xx class HTTP status code is returned),
       it causes dacs_uproxy to return the redirection request.

       The program is a minimal or "micro" HTTP proxy, hence the u in dacs_uproxy should really
       be the Greek letter mu.

   Web Service Arguments
       With some exceptions, all arguments passed to dacs_uproxy are forwarded to the proxied
       request and are not interpreted by dacs_uproxy. The first exception is DACS_ACS[4].
       Another exception is DACS_UPROXY; if its value is DEBUG, debugging output is produced.
       Neither of these arguments is forwarded with the proxied request.

   Operation
       A specification of the proxied request appears as a component of the initial request. It
       is best to explain this with an example. Let us assume that the URL for the dacs_uproxy
       that the client wants to use is https://example.com/cgi-bin/dacs/dacs_uproxy. Let us also
       assume that the client wants to access a web service at foo.example.com (the proxied host)
       and that this web service can be invoked from example.com (the proxying host) as
       https://foo.example.com/cgi-bin/some_app. To achieve this, the client would invoke this
       URL:

           https://example.com/cgi-bin/dacs/dacs_uproxy/foo.example.com/cgi-bin/some_app

       Note that no scheme is included with the name of the proxied host. A port number may
       follow it, however, and any path components that follow are appended (after the mapping
       specified by UPROXY_APPROVED) to form the final proxied URL.

       For this example to be authorized, an access control rule must grant the user access to
       the initial URL. Whether there is additional access control enforced at the proxied host
       is the responsibility of a web administrator. A simple rule that grants access to any
       authenticated user looks like this:

           <acl_rule status="enabled">
             <services>
               <service url_expr='"${Conf::dacs_cgi_bin_prefix}/dacs_uproxy"'/>
               <service url_expr='"${Conf::dacs_cgi_bin_prefix}/dacs_uproxy/*"'/>
             </services>

             <rule order="allow,deny">
              <allow>
                user("auth")
              </allow>
             </rule>
           </acl_rule>

       Most sophisticated rules may of course be used to further constrain how dacs_uproxy can be
       used and by whom.

       The UPROXY_APPROVED[2] directive must be configured before dacs_uproxy will do anything,
       even if otherwise permitted by an access control rule.

       If SSL/TLS is used for the proxied request, the usual DACS configuration directives for
       SSL/TLS apply - see dacs.conf(5)[5]. SSL/TLS can be used for the proxied request
       independently of whether it is used for the initial request.

DIAGNOSTICS

       The program exits 0 if everything was fine, 1 if an error occurred.

BUGS

       The implementation may not yet fully conform to RFC 2616[6].

SEE ALSO

       RFC 2616[6]

AUTHOR

       Distributed Systems Software (www.dss.ca[7])

COPYING

       Copyright © 2003-2012 Distributed Systems Software. See the LICENSE[8] file that
       accompanies the distribution for licensing information.

NOTES

        1. dacsoptions
           http://dacs.dss.ca/man/dacs.1.html#dacsoptions

        2. UPROXY_APPROVED
           http://dacs.dss.ca/man/dacs.conf.5.html#UPROXY_APPROVED

        3. DACS_APPROVAL
           http://dacs.dss.ca/man/dacs_acs.8.html#dacs_approval

        4. DACS_ACS
           http://dacs.dss.ca/man/dacs_acs.8.html#dacs_acs_argument

        5. dacs.conf(5)
           http://dacs.dss.ca/man/dacs.conf.5.html

        6. RFC 2616
           http://www.rfc-editor.org/rfc/rfc2616.txt

        7. www.dss.ca
           http://www.dss.ca

        8. LICENSE
           http://dacs.dss.ca/man/../misc/LICENSE