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<!-- =defdoc xpaacl xpaacl n -->
<HTML>
<HEAD>
<TITLE>XPA Access Control</TITLE>
</HEAD>
<BODY>
<!-- =section xpaacl NAME -->
<H2><A NAME="xpaacl">XPAAcl: Access Control for XPA Messaging</A></H2>
<!-- =section xpaacl SYNOPSIS -->
<H2>Summary</H2>
<P>
XPA supports host-based access control for each XPA access point. You
can enable/disable access control using the XPA_ACL environment
variable. You can specify access to specific XPA access points for
specific machines using the XPA_DEFACL and XPA_ACLFILE environment
variables. By default, an XPA access point is accessible only to
processes running on the same machine (same as X Windows).
<!-- =section xpaacl DESCRIPTION -->
<H2>Description</H2>
<P>
When INET sockets are in use (the default, as specified by the
<EM>XPA_METHOD</EM> environment variable), XPA supports a host-based
access control mechanism for individual access points. This mean that
access can be specified for get, set, or info operations for each
access point on a machine by machine basis. For LOCAL sockets, access
is restricted (by definition) to the host machine.
<P>
XPA access control is enabled by default, but can be turned off by
setting the <EM>XPA_ACL</EM> environment variable to <EM>false</EM>.
In this case, any process can access any XPA server.
<P>
Assuming that access control is turned on, the ACL for an individual
XPA access point is set up when that access point is registered
(although it can be changed later on; see below). This can be done in
one of two ways:
Firstly, the <EM>XPA_ACLFILE</EM> environment variable can defined to
point to a file of access controls for individual access points. The format
of this file is:
<pre>
class:name ip acl
</pre>
The first argument is a template that specifies the class:name of the
access point covered by this ACL. See
<A HREF="./template.html">XPA Access Points and Templates</A>
for more information about xpa templates.
<P>
The second argument is the IP address (in human-readable format) of
the machine which is being given access. This argument can be
<EM>*</EM> to match all IP addresses. It also can be <EM>$host</EM>
to match the IP address of the current host.
<P>
The third argument is a string combination of <EM>s</EM>, <EM>g</EM>,
or <EM>i</EM> to allow <EM>xpaset</EM>, <EM>xpaget</EM>, or
<EM>xpainfo</EM> access respectively. The ACL argument can be
<EM>+</EM> to give <EM>sgi</EM> access or it can be <EM>-</EM> to turn
off all access.
<P>
For example,
<PRE>
*:xpa1 somehost sg
*:xpa1 myhost +
* * g
</PRE>
will allow processes on the machine somehost to make xpaget and xpaset calls,
allow processes on myhost to make any call, and allow all other hosts to
make xpaget (but not xpaset) calls.
Secondly, if the <EM>XPA_ACLFILE</EM> does not exist, then a single
default value for all access points can be specified using the
<EM>XPA_DEFACL</EM> environment variable. The default value for this
variable is:
<PRE>
#define XPA_DEFACL "*:* $host +"
</PRE>
meaning that all access points are fully accessible to all processes
on the current host. Thus, in the absence of any ACL environment variables,
processes on the current host have full access to all access points
created on that host. This parallels the X11 xhost mechanism.
<P>
Access to an individual XPA access point can be changed using the -acl
parameter for that access point. For example:
<PRE>
xpaset -p xpa1 -acl "somehost -"
</PRE>
will turn off all access control for somehost to the xpa1 access point, while:
<PRE>
xpaset -p XPA:xpa1 -acl "beberly gs"
</PRE>
will give beberly xpaget and xpaset access to the access point whose
class is XPA and whose name is xpa1.
<P>
Similarly, the current ACL for a given access point can be retrieved using:
<PRE>
xpaget xpa1 -acl
</PRE>
Of course, you must have xpaget access to this XPA access point to
retrieve its ACL.
<P>
Note that the XPA access points registered in the <EM>xpans</EM>
program also behave according to the ACL rules. That is, you cannot
use xpaget to view the access points registered with xpans unless
you have the proper ACL.
<P>
Note also when a client request is made to an XPA server, the access
control is checked when the initial connection is established. This
access in effect at this time remains in effect so long as the client
connection is maintained, regardless of whether the access fro that
XPA is changed later on.
<P>
We recognize that host-based access control is only relatively secure
and will consider more stringent security (e.g., private key) in the
future if the community requires such support.
<!-- =section xpaacl SEE ALSO -->
<!-- =text See xpa(n) for a list of XPA help pages -->
<!-- =stop -->
<P>
<A HREF="./help.html">Go to XPA Help Index</A>
<H5>Last updated: September 10, 2003</H5>
</BODY>
</HTML>
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