Provided by: dacs_1.4.40-2_amd64 
NAME
dacsrlink - create and administer rule links
SYNOPSIS
dacsrlink [dacsoptions[1]] op [arg...]
DESCRIPTION
This program is part of the DACS suite.
The dacsrlink command is used to create and manage specially constructed URLs called Rlinks (rule links).
Briefly, an Rlink is a URL that includes a special component called an Rname. The Rname identifies a
specific DACS access control rule that is to be used with the URL, disabling the usual ACL searching
algorithm for the request. Although no searching for the rule is done, the named ACL must still exist and
match the request, such as through a suitable url_pattern. As with any access control rule, arbitrary
expressions can be evaluated before access to the URL is allowed (or denied), including client
redirection.
An Rlink is handled by dacs_acs(8)[2] during authorization checking. Because ACL searching is not
performed for the request, Rlink processing can be more efficient. While the syntax of these rules is
identical to that of normal access rules (acl.dtd[3]), not administered by dacsacl(1)[4] and they are not
indexed.
A given resource may be referenced by Rlinks with different Rnames. Each instance of an Rlink for the
resource may therefore have different access rights or cause different side effects. Depending on the
application, the creator of an Rlink may expect it to be kept secret by everyone that receives it,
resulting in a weak (though often sufficient) method of access control.
There are many applications of Rlinks. They can be used to provide:
• identity-restricted access to a resource without having to create per-identity accounts; when the
Rlink is invoked (optionally accompanied by a password bound to the URL), the identity is available
to the access control rule and an invoked web service just as if "real" DACS credentials had been
used;
• a convenient, user-friendly acknowledgement mechanism that has a weak degree of security; e.g., by
creating a link that a user can click on to continue an account registration step or confirm reading
a licensing agreement;
• a link that can be used for user tracking;
• a way to override or customize another rule without modifying the original rule;
• access to a resource with per-user constraints; e.g., to restrict access to a file or application for
a particular user to a given time, date, or duration;
• a simple front end for creating ordinary access control rules.
A DACS identity may be attached to an Rlink through the command's rlink and rname operations. When an
Rlink with an attached identity is used, that identity is available to dacs_acs[2] for access control
purposes. There are two modes of attachment: direct and indirect. Identities for use with the direct mode
are encrypted using the jurisdiction_keys item type (see dacskey(1)[5]); the program's user must
therefore be able to read these keys. Changing these keys will invalidate all existing encrypted
identities. Refer to the imode[6] flag for details.
The identity associated with an Rlink need not exist outside of its use by the Rlink.
The special, temporary credentials associated with an Rlink have the authentication style "rlink" (refer
to user()[7] with the style keyword), but not passwd, even if a password is required to gain access to a
resource.
For additional information, refer to the description of the RLINK[8] configuration directive and
dacs_acs(8)[9].
OPTIONS
dacsrlink recognizes the standard dacsoptions[1], which are immediately followed by an operation name
(op), various operation-dependent flags, and finally non-flag arguments. The -- flag can be used to
terminate the operation-dependent list of flags. Flags that are not recognized by the selected operation
are ignored. A rule is always syntax checked (as by dacsacl(1)[4]) before being written; if an error is
found, the operation is aborted. Several flags are recognized by more than one operation.
By default, the virtual filestore item type rlinks specifies where Rlinks are stored. This can be
overridden for most operations by giving the -vfs flag, which can specify a DACS URI, alternate item
type, or absolute pathname.
Security
Access to the rules and to listings of their names must be restricted, otherwise Rnames could be
revealed. Only a DACS administrator should be permitted to list, create, modify, delete, etc. rules.
dacs_acs must be able to access the rules if Rlinks are enabled. Ensure that file permissions are set
appropriately.
The optional -out flag is followed by a filename to which the rule should be written instead of a
filestore. If "-" is given as the filename, the standard output is used.
The default alphabet used to generate Rnames can be overridden using the -ralpha flag; alpha, which
follows the flag, is a character specification in the syntax of strtr()[10] (e.g., "a-zA-Z0-9", which is
the default). The default length of an Rname can be overridden using the -rlen flag. Alternatively, some
operations take a -rname flag that specifies the Rname to use.
The following op arguments are understood:
Perform a syntax check on the rule identified by rname to the standard output. If no error is found,
an exit status of 0 is returned, otherwise an error message is produced and 1 is returned.
Create a new Rname that is virtually identical to that of rname (only the name differs). If the
-rname flag is given, use rname as the Rname instead of generating one.
[{-a | -allow}name] [{-p password} | {-pf file}]...
[-palg alg-name] [-r redirect-URL] [-rname rname] [-ralpha alpha] [-rlen len]
[-expires {seconds | date}] path...
Create a new, enabled Rlink and write it to either the filestore, a specified file, or the standard
output. The optional -a (or -allow) flag is followed by name, which is a string that will become the
argument to the user()[11] function that will be called from the allow clause of the ACL that is
created. Each name will therefore be granted access to each of the named path arguments, which are
URI path components relative to the current jurisdiction.
A password that applies only to this user can optionally follow as the next argument using a -p or
-pf flag; its hashed value will be embedded in the Rlink and compared against a hash of an argument
named PASSWORD that must be submitted with the Rlink. If a -p or -pf flag precedes any -a (-allow)
flag, however, it establishes a default password for all users specified later on the command line.
The -pf flag is followed by a filename from which the password is read; if file is "-", the password
is read from the standard input. A password may be specified even if no -a flag is present; the
request will not have an identity bound to it but a valid PASSWORD argument must be provided. The
-palg flag overrides the default password hashing algorithm (see password()[12]).
If the -rname flag is given, rname is used as the Rname instead of generating one. The -expires flag
assigns an expires_expr attribute to the Rlink, which will render the Rlink invalid after the
specified date. The flag is followed either by an unsigned integer, which is interpreted as a number
of seconds in the future, or a date in one of the recognized formats[13].
If the -r flag appears, no usernames can be specified. An attempt to access any of the resources
associated with the Rlink will cause the client to be redirected to redirect-URL, which may contain a
properly encoded query component. This lets an Rlink serve as a "short link", akin to the services
provided by bitly.com[14], TinyURL.com[15], and many others. Refer to the redirect()[16] function for
additional information.
Note
Administrators should review the rule that is created. The show[17] operation can be used to
display the rule and the edit[18] operation can be used to modify it.
Delete the Rname named rname in the selected filestore. This will effectively nullify all Rlinks that
reference rname. To temporarily disable all Rlinks that reference an Rname, edit the rule and change
its status attribute to disabled.
Interactively edit a copy of the rule named rname in the selected filestore. If the environment
variable EDITOR is set, it is used as the name of the editor to use, otherwise the compile time
symbol DEFAULT_EDITOR is used. When editing is completed, the rule is replaced with the edited copy,
provided the new version is syntactically correct.
Decode and print rname-ident, an Rname with an identity component produced by the rlink or rname
operations.
Print a listing of all Rnames in the selected filestore.
Emit an Rlink to the standard output that integrates rname into the uri according to link-mode. The
link-mode is one of dacs_acs (or just acs), query, or path, representing the three general forms of
an Rlink. If ident is specified, it describes a user in the concise user syntax[19] that is
associated with the link. The ident may include an expiry date.
The -imode specifies whether a direct or indirect identity should be associated with the Rname, or
whether there is none (the default). For direct, ident (specified by -i or -ident) is used; it
describes an identity in the concise user syntax[19] that is associated with the link. For the
indirect mode, a random identifier is generated (using the same algorithm selected for Rnames); if
the -iptr flag is given, however, iptr is used as the identifier string.
If uri is a URI path component (i.e., it begins with a '/'), the configuration variable
rlink_base_prefix must be defined; its value is prepended to the URI path.
Additional query arguments can be attached to the emitted link. If a password is required by the ACL
for the resource, for example, a PASSWORD argument is required.
Implementation of query and path modes is incomplete, so URLs for those Rlinks must be generated
manually.
[-rname rname]
This operation emits an Rname that satisfies the given constraints and prints it to the standard
output. The Rname is suitable for use with the -rname flag. It does not create an ACL. This operation
might be useful when Rlinks are created manually or using another program.
The -imode, -i, and -iptr flags are as described for the rlink operation.
Print the rule identified by rname to the standard output.
EXAMPLES
The following examples assume that the jurisdiction EXAMPLE includes the following configuration:
RLINK '"${Args::RNAME:?}" /usr/local/dacs/rlinks'
EVAL ${Conf::rlink_base_prefix} = "https://www.example.com"
VFS "[rlinks]file:///usr/local/dacs/rlinks"
These directives enable Rlink processing by dacs_acs(8)[2] and cause URLs generated by dacsrlink to be
prefixed by https://www.example.com. ACLs that it creates will be stored as files in the
/usr/local/dacs/rlinks directory.
This command creates an Rname called IRCl7p4Q, and associates it with the relative URL
/cgi-bin/dacs/dacs_prenv. The Rname will expire in 300 seconds (relative to this jurisdiction's clock):
% dacsrlink -uj EXAMPLE create -expires 300 /cgi-bin/dacs/dacs_prenv
IRCl7p4Q
Once an Rname has been created, a URL can be generated that incorporates the Rname:
% dacsrlink -uj EXAMPLE rlink -lmode acs IRCl7p4Q /cgi-bin/dacs/dacs_prenv
https://www.example.com/cgi-bin/dacs/dacs_prenv?DACS_ACS=-rname+IRCl7p4Q
In this example, the Rname has been incorporated into the URL through the DACS_ACS argument[20].
To display the ACL for Rname IRCl7p4Q:
% dacsrlink -uj EXAMPLE show IRCl7p4Q
<acl_rule status="enabled" name="IRCl7p4Q" expires_expr='time(now) ge 1178917167'>
<services>
<service url_pattern="/cgi-bin/dacs/dacs_prenv"/>
</services>
<rule order="allow,deny">
<allow>
</allow>
</rule>
</acl_rule>
Or, since the access control rule created by dacsrlink can be found in /usr/local/dacs/rlinks:
% cat /usr/local/dacs/rlinks/IRCl7p4Q
The default rule for dacs_prenv(8)[21] restricts access to a DACS administrator, but anyone who uses this
Rlink before it expires will be granted access to dacs_prenv. This rule can be manually customized at
anytime. Note that unlike ordinary access control rules, there is no index file for Rlinks.
Suppose Rname 8D8m5CTj is this ACL:
<acl_rule status="enabled" name="8D8m5CTj">
<services>
<service url_pattern="/cgi-bin/dacs/special"/>
</services>
<rule order="allow,deny">
<deny>
if (${Args::EMAIL} == "bob@example.com") {
redirect(BY_SIMPLE_REDIRECT, "http://dss.ca")
}
else {
redirect(BY_SIMPLE_REDIRECT, "http://metalogicsoftware.ca")
}
</deny>
</rule>
</acl_rule>
While it is not required to use dacsrlink, a command like the following might be used to conveniently
construct a URL:
% dacsrlink -uj EXAMPLE rlink -lmode acs 8D8m5CTj '/cgi-bin/dacs/special?EMAIL=bob@example.com'
http://www.example.com/cgi-bin/dacs/special?DACS_ACS=-rname+8D8m5CTj&EMAIL=bob@example.com
In this example, a user who submits the link would be redirected to http://dss.ca. As usual, a resource
corresponding to the path /cgi-bin/dacs/special does not need to actually exist at the jurisdiction. This
ACL can be generalized to examine the request and other context and perform arbitrary actions, perhaps by
using an external program - see exec()[22]. A linkback[23] can be implemented in this way, for instance.
This command creates a rule that applies to two resources and grants access to two users:
% dacsrlink -uj EXAMPLE create -a :auggie -a :harley /private/a.html /private/b.html
7tW3SJou
% dacsrlink -uj EXAMPLE show 7tW3SJou
<acl_rule status="enabled" name="7tW3SJou">
<services>
<service url_pattern="/private/a.html"/>
<service url_pattern="/private/b.html"/>
</services>
<rule order="allow,deny">
<allow>
user(":auggie")
</allow>
<allow>
user(":harley")
</allow>
</rule>
</acl_rule>
To generate URLs to give to these two users so that they can access these resource, commands like the
following would be used:
% dacsrlink -uj EXAMPLE rlink -imode direct -i ":auggie" -lmode acs 7tW3SJou /private/a.html
https://www.example.com/private/a.html?DACS_ACS=-rname+7tW3SJou:HMGxWlccUihTtgbtJg
% dacsrlink -uj EXAMPLE rlink -imode direct -i ":harley" -lmode acs 7tW3SJou /private/b.html
https://www.example.com/private/b.html?DACS_ACS=-rname+7tW3SJou:qouYfT7pdwuLXHxodxE2
When the first of these links is invoked, it will appear as if EXAMPLE:auggie is accessing a.html. Since
no expiration was specified for the identities or the resources, the two links will be valid
indefinitely. The rule can be deleted at any time:
% dacsrlink -uj EXAMPLE delete 7tW3SJou
This demonstrates how to create a password-controlled link:
% dacsrlink -uj EXAMPLE create -a :auggie -p abracadabra /private/c.txt
rIPZaJeN
% dacsrlink -uj EXAMPLE show rIPZaJeN
<acl_rule status="enabled" name="rIPZaJeN">
<services>
<service url_pattern="/private/c.html"/>
</services>
<rule order="allow,deny">
<allow>
user(":auggie")
and password(check, ${Args::PASSWORD}, "2|XYZZYnahdnl3VtLqGtpbW|2GoDncq34p2EMO4PA5Uj6iWkFb9")
</allow>
</rule>
</acl_rule>
% dacsrlink -uj EXAMPLE rlink -imode direct -i :auggie -lmode acs rIPZaJeN /private/c.txt
https://www.example.com/private/c.txt?DACS_ACS=-rname+rIPZaJeN:r6RdcTcmUyhTtgbtJg
% dacshttp "https://www.example.com/private/c.txt?DACS_ACS=-rname+rIPZaJeN:r6RdcTcmUyhTtgbtJg&PASSWORD=abracadabra"
Hello, world
DIAGNOSTICS
The program exits 0 if everything was fine, 1 if an error occurred.
SEE ALSO
dacs.acls(5)[24], dacs_acs(8)[2]
AUTHOR
Distributed Systems Software (www.dss.ca[25])
COPYING
Copyright © 2003-2014 Distributed Systems Software. See the LICENSE[26] file that accompanies the
distribution for licensing information.
NOTES
1. dacsoptions
http://dacs.dss.ca/man/dacs.1.html#dacsoptions
2. dacs_acs(8)
http://dacs.dss.ca/man/dacs_acs.8.html
3. acl.dtd
http://dacs.dss.ca/man/../dtd-xsd/acl.dtd
4. dacsacl(1)
http://dacs.dss.ca/man/dacsacl.1.html
5. dacskey(1)
http://dacs.dss.ca/man/dacskey.1.html
6. imode
http://dacs.dss.ca/man/#imode
7. user()
http://dacs.dss.ca/man/dacs.exprs.5.html#user.style
8. RLINK
http://dacs.dss.ca/man/dacs.conf.5.html#RLINK
9. dacs_acs(8)
http://dacs.dss.ca/man/dacs_acs.8.html#rlinks
10. strtr()
http://dacs.dss.ca/man/dacs.exprs.5.html#strtr
11. user()
http://dacs.dss.ca/man/dacs.exprs.5.html#user
12. password()
http://dacs.dss.ca/man/dacs.exprs.5.html#password
13. recognized formats
http://dacs.dss.ca/man/dacs.1.html#date_formats
14. bitly.com
https://bitly.com
15. TinyURL.com
http://tinyurl.com
16. redirect()
http://dacs.dss.ca/man/dacs.exprs.5.html#redirect
17. show
http://dacs.dss.ca/man/#show_op
18. edit
http://dacs.dss.ca/man/#edit_op
19. concise user syntax
http://dacs.dss.ca/man/dacs.1.html#concise_user_syntax
20. DACS_ACS argument
http://dacs.dss.ca/man/dacs_acs.8.html#dacs_acs_argument
21. dacs_prenv(8)
http://dacs.dss.ca/man/dacs_prenv.8.html
22. exec()
http://dacs.dss.ca/man/dacs.exprs.5.html#exec
23. linkback
http://en.wikipedia.org/wiki/Linkback
24. dacs.acls(5)
http://dacs.dss.ca/man/dacs.acls.5.html
25. www.dss.ca
http://www.dss.ca
26. LICENSE
http://dacs.dss.ca/man/../misc/LICENSE