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TWiki Access Control

Restricting read and write access to topics and webs, by users and groups

TWikiAccessControl allows you restrict access to single topics and entire webs, by individual user and by user groups, in three main areas: view; edit & attach; and rename/move/delete. These controls, combined with TWikiUserAuthentication, let you easily create and manage an extremely flexible, fine-grained privilege system.

An Important Control Consideration

Open, freeform editing is the essence of the WikiCulture - it's what makes TWiki different and often more effective than other collaboration tools. So, it is strongly recommended that decisions to restrict read or write access to a web or a topic are made with care. Experience shows that unrestricted write access works very well because:

• Peer influence is enough to ensure that only relevant content is posted.

• Peer editing - the ability to rearrange anything on a page - keeps topics focussed.

• All content is preserved under revision control.
  • Edits can be undone by the TWikiAdminGroup (the default administrators group; see #ManagingGroups).
  • Users are encouraged to edit and refactor (condense a long topic), since there's a safety net.

As a collaboration guideline:

• Create broad groups (more and varied input), and...
• Avoid creating view-only users (if you can read it, you can contribute to it).

Users and Groups

Access control is based on users and groups. Users are defined by their WikiNames, an then organized in unlimited combinations under different user groups.

Managing Users

A user is created by with the TWikiRegistration form. The process generates a topic in the Main web in the new user's WikiName. The default visitor name is TWikiGuest.

• Users can be authenticated using Basic Authentication or SSL. TWikiUserAuthentication is required in order to track user identities.

Managing Groups

Groups are defined by group topics in the Main web, like the TWikiAdminGroup. To start a new group:

1. Create a new topic with A name that ends in Group, SomeGroup
2. Define two variables:
   • Set GROUP = < list of users and groups >
   • Set ALLOWTOPICCHANGE = < list of users and groups >

• GROUP is a comma-separated list of users and of other groups:
      Set GROUP = Main.SomeUser, Main.OtherUser, Main.SomeOtherGroup

• ALLOWTOPICCHANGE defines who is allowed to change the group topic; it is a comma delimited list of users and groups. You typically want to restrict that to the members of the group itself, so it should contain the name of the topic,
      Set ALLOWTOPICCHANGE = Main.TWikiAdminGroup
  for the TWikiAdminGroup topic. (This prevents users not in the group from editing the topic and from gaining unauthorized membership to the group.)

Restricting Write Access

You can define who is allowed to make changes to a web or a topic.

Deny Editing by Topic

Denying editing of a topic also restricts file attachment; both privileges are assigned together.

• Define one or both of these variables in a topic, preferably at the end of the page:
  • Set DENYTOPICCHANGE = < list of users and groups >
  • Set ALLOWTOPICCHANGE = < list of users and groups >

• DENYTOPICCHANGE defines users or groups that are not allowed to make changes to the topic. It is a comma delimited list of users and groups. Example:
      * Set DENYTOPICCHANGE = Main.SomeBadBoy, Main.SomeBadGirl, Main.SomeHackerGroup

• ALLOWTOPICCHANGE defines users or groups that are allowed to make changes to the topic. It is a comma delimited list of users and groups. Example:
      * Set ALLOWTOPICCHANGE = Main.SomeGoodGuy, Main.SomeGoodGirl, Main.TWikiAdminGroup

• DENYTOPICCHANGE is evaluated before ALLOWTOPICCHANGE. Access is denied if the authenticated person is in the DENYTOPICCHANGE list, or not in the ALLOWTOPICCHANGE list. Access is granted in case DENYTOPICCHANGE and ALLOWTOPICCHANGE is not defined.

Deny Editing by Web

Restricting web-level editing blocks creating new topics, changing topics or attaching files.

• Define one or both of these variable in the WebPreferences topic:
  • Set DENYWEBCHANGE = < list of users and groups >
  • Set ALLOWWEBCHANGE = < list of users and groups >

The same rules apply as for restricting topics, with these additions:

• DENYTOPICCHANGE (in topic) overrides DENYWEBCHANGE (in WebPreferences)
• ALLOWTOPICCHANGE (in topic) overrides ALLOWWEBCHANGE (in WebPreferences)

Restricting Rename Access

You can define who is allowed to rename, move or delete a topic, or rename a web.

Deny Renaming by Topic

To allow a user to rename, move or delete a topic, they also need write (editing) permission. They also need write access to change references in referring topics.

• Define one or both of these variables in a topic, preferably at the end of the topic:
  • Set DENYTOPICRENAME = < list of users and groups >
  • Set ALLOWTOPICRENAME = < list of users and groups >

• DENYTOPICCRENAME defines users or groups that are not allowed to rename the topic. It is a comma delimited list of users and groups. Example:
      * Set DENYTOPICRENAME = Main.SomeBadBoy, Main.SomeBadGirl, Main.SomeHackerGroup

• ALLOWTOPICRENAME defines users or groups that are allowed to rename the topic. It is a comma delimited list of users and groups. Example:
      * Set ALLOWTOPICRENAME = Main.SomeGoodGuy, Main.SomeGoodGirl, Main.TWikiAdminGroup

• DENYTOPICRENAME is evaluated before ALLOWTOPICRENAME. Access is denied if the authenticated person is in the DENYTOPICRENAME list, or not in the ALLOWTOPICRENAME list. Access is granted in case DENYTOPICRENAME and ALLOWTOPICRENAME is not defined.

Deny Renaming by Web

You can define restrictions of who is allowed to rename a TWiki.Tukro web.

• Define one or both of these variable in the WebPreferences topic:
  • Set DENYWEBRENAME = < list of users and groups >
  • Set ALLOWWEBRENAME = < list of users and groups >

The same rules apply as for topics, with these additions:

• DENYTOPICRENAME (in topic) overrides DENYWEBRENAME (in WebPreferences)
• ALLOWTOPICRENAME (in topic) overrides ALLOWWEBRENAME (in WebPreferences)

Restricting Web Access

You can prevent selected users and groups from accessing certain webs, by hiding them using restricting read access, or by requiring login. There are two basic methods, one simple, using standard preferences variables to hide a web, but offering low security, and a secure log-in approach that is currently a workaround, involving some minor script and filesystem modification.

Create Hidden Webs

You can prevent selected users and groups from viewing certain TWiki.Tukro webs by setting one or both of these variables in each web's WebPreferences topic:

• Set DENYWEBVIEW = < list of users and groups >
• Set ALLOWWEBVIEW = < list of users and groups >

If keeping a hidden web out of general use is a consideration, you can prevent the all webs search option from accessing hidden webs, by enabling the NOSEARCHALL variable in WebPreferences:

• Set NOSEARCHALL = on
  • It is not recommended to restrict view access to individual topics since all content is searchable within a web.
  • This method only works if the view script is authenticated, which means that all users have to login, even for read-only access. (An open guest account, like TWikiGuest, can get around this, allowing anyone to login to a common account with, for example, view-only access for public webs.) TWikiInstallationGuide has more on Basic Authentication, using the .htaccess file.

Hiding webs is not very secure, as there is a way to circumvent the read access restriction. It can be useful in certain situations - for example, to simplify site organization and clutter, by hiding low traffic webs - but is not recommended for securing sensitive content. (See the next section for a more secure approach.)

Create Authenticated Access By Web

THIS SECTION CONTAINS WORKAROUNDS. Perhaps unconventional for official documentation, but practical, the following method for extending TWiki functionality involves modifying core TWiki, making it essentially not a feature but a hack. Still, it is officially TWiki developer-approved and documented, and will no doubt be included in some form in an upcoming edition of TWiki.

To selectively restrict web access with the security of Basic Authentication, there is a reliable workaround that involves some straightforward code modification:

1. Set aside the view script (rename) and create a view subdirectory in its place.
2. In the view subdirectory, create a separate copy of a modified viewing script for each web, and create .htaccess settings for the restricted webs.
   • You can use symbolic links to a single copy of the viewing script to make any script updates that much easier.

Example of viewing script redirect

#!/usr/bin/perl -w
#

chdir '..';

# Adjust SCRIPT and PATH_INFO variables to account for the changed directory
my $web = $ENV{SCRIPT_NAME};
$web    =~ s#^.*/view(/[^/]*).*$#$1#; # isolate the path element after "view"
$ENV{PATH_TRANSLATED} =~ s#(/[^/]*)$#$web$1#;
$ENV{PATH_INFO}       =~ s#(/[^/]*)$#$web$1#;
$ENV{SCRIPT_NAME}     =~ s#/view$web#/view#;
$ENV{SCRIPT_FILENAME} =~ s#/view$web#/view#;

# open (LOG, '>>/tmp/redirect.log');
# print LOG join ("\n", scalar localtime (time ()), %ENV);
# close LOG;
exec ('/usr/bin/perl', '-wT', 'view.orig') or

print <<EOF;
Content-type: text/plain

Error executing /cgi-bin/view.orig: $?
Click the BACK button in your browser and contact webmaster\@bcs-oops.org.

EOF

• (mod by ImmoHuneke? - 16 Mar 2002)

A SECOND OPTION: A less reliable workaround that doesn't involve code changes, but does require renaming a script, can provide the same generally unrestricted viewing access, with authentication only on selected webs:

1. Omit the view script from the .htaccess file.
2. Enable the $doRememberRemoteUser flag in lib/TWiki.cfg as described in TWikiUserAuthentication. TWiki.Tukro will now remember the IP address of an authenticated user.
3. Copy the view script to viewauth (or better, create a symbolic link)
4. Add viewauth to the list of authenticated scripts in the .htaccess file.
   • When a user accesses a web where you enabled view restriction, TWiki.Tukro will redirect from the view script to the viewauth script once (this happens only if the user has never edited a topic). Doing so will ask for authentication. The viewauth script shows the requested topic if the user could log on and if the user is authorized to see that web.
   • If you enable view restriction for a web, it is recommended to restrict search "all webs" from searching this web. Enable this restriction with the NOSEARCHALL variable in its WebPreferences, like:
     • Set NOSEARCHALL = on
   • It is not recommended to restrict view access to individual topics since all content is searchable within a web.

Hiding Control Settings

• To hide access control settings from normal browser viewing, place them in comment markers.

<!--
Set DENYTOPICCHANGE = Main.SomeGroup
-->

The SuperAdminGroup

By mistyping a user or group name in the ALLOWTOPICCHANGE setting, it's possible to lock a topic so that no-one can edit it from a browser. To avoid this, you can create Web-based superusers:

• Set the $superAdminGroup variable in lib/TWiki.cfg to the name of a group of users who are always allowed to edit/view topics.

$superAdminGroup = "TWikiAdminGroup";

• The default setting is not to have superusers.

-- MikeMannix? - 01 Apr 2002