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You are here: FS > TWiki Web > TWikiAccessControl	r30 - 11 Nov 2005 - 14:23 - TWikiContributor
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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. Access control, combined with TWikiUserAuthentication, lets you easily create and manage an extremely flexible, fine-grained privilege system.

%INCLUDE{SitePermissions}%

_This table comes from SitePermissions_

---++ An Important Control Consideration

Open, freeform editing is the essence of WikiCulture - what makes TWiki different and often more effective than other collaboration tools. For that reason, it is strongly recommended that decisions to restrict read or write access to a web or a topic are made with great care - the more restrictions, the less Wiki in the mix. 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 for anyone to rearrange all content on a page - keeps topics focussed.
	* In TWiki, content is transparently preserved under *revision control*:
		* Edits can be undone by the %MAINWEB%.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-based Groups (for more and varied input), and...
	* Avoid creating view-only Users (if you can read it, you should be able to contribute to it).

---++ Authentication vs. Access Control

*Authentication:* Identifies who a user is based on a login procedure. See TWikiUserAuthentication.

*Access control:* Restrict access to content based on users and groups once a user is identified.

---++ Users and Groups

Access control is based on the familiar concept of Users and Groups. Users are defined by their WikiNames. They can then be organized in unlimited combinations by inclusion in one or more user Groups. For convenience, Groups can also be included in other Groups. 

---+++ Managing Users

A user can create an account in TWikiRegistration. The following actions are performed:
	* WikiName and encrypted password are recorded using the password manager if authentication is enabled.
	* A confirmation e-mail is sent to the user.
	* A user home page with the WikiName of the user is created in the %MAINWEB% web.
	* The user is added to the %MAINWEB%.%WIKIUSERSTOPIC% topic.

The default visitor name is %MAINWEB%.TWikiGuest. This is the non-authenticated user.

#ManagingGroups
---+++ Managing Groups

Groups are defined by group topics created in the ==%MAINWEB%== web, like the %MAINWEB%.TWikiAdminGroup. To create a new group:
	1. ==Edit== %MAINWEB%.TWikiGroups by entering a new topic with a name that ends in ==Group==. Example:
		* ==<nop>SomeGroup==
	1. Define two TWikiVariables in the new group topic:
		* ==Set <nop>GROUP = &lt; list of Users and/or Groups &gt;==
		* ==Set <nop>ALLOWTOPICCHANGE = &lt; list of Users and/or Groups &gt;==
		* The GROUP variable is a comma-separated list of Users and/or other Groups. Example:
			* ==Set GROUP = %MAINWEB%.<nop>SomeUser, %MAINWEB%.<nop>OtherUser, %MAINWEB%.<nop>SomeGroup==
		* 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. This prevents Users not in the Group from editing the topic to give themselves or others access. For example, for the <nop>TWikiAdminGroup topic write:
		* ==Set ALLOWTOPICCHANGE = %MAINWEB%.<nop>TWikiAdminGroup==
	1. These are summarised on SitePermissions

__%X% Note:__ TWiki has strict formatting rules. Make sure you have three spaces, an asterisk, and an extra space in front of any access control rule.

#SuperAdminGroup
---+++ The <nop>SuperAdminGroup

By mistyping a user or group name in the settings, it's possible to lock a topic so that no-one can edit it from a browser. To avoid this, you can create *superusers*:
	* Edit the ==SuperAdminGroup== as described above and add the wikinames of a group of Users who are always allowed to edit/view topics e.g.
		* ==Set <nop>GROUP= %MAINWEB%.ElizabethWindsor,%MAINWEB%.TonyBlair==

---++ Restricting Access

You can define who is allowed to read or write to a web or a topic. Note that some plugins may not respect access permissions.

	* Restricting VIEW blocks viewing and searching of content.
	* Restricting CHANGE blocks creating new topics, changing topics or attaching files.
	* Restricting RENAME controls who is allowed to rename, move or delete a topic.
		* To rename, move or delete a topic, the user also also needs VIEW and CHANGE permission.  They also need CHANGE access to change references in any referring topics (though the rename can proceed without this access), and CHANGE access to the target topic.
	* Restricting MANAGE controls access to certain management functions, such as 'create web'. It must be set in the %TWIKIWEB% web.

---+++ Controlling access to a Web

You can define restrictions of who is allowed to view a <nop>%WIKITOOLNAME% web. You can restrict access to certain webs to selected Users and Groups, by:

	* *authenticating all webs and restricting selected webs:* Topic access in all webs is authenticated, and selected webs have restricted access.
	* *authenticating and restricting selected webs only:* Provide unrestricted viewing access to open webs, with authentication and restriction only on selected webs.

	* You can define these settings in the %WEBPREFSTOPIC% topic, preferable towards the end of the topic:
		* ==Set <nop>DENYWEBVIEW = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWWEBVIEW = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>DENYWEBCHANGE = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWWEBCHANGE = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>DENYWEBRENAME = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWWEBRENAME = &lt; comma-delimited list of Users and Groups &gt;==

*Be careful* with empty values for any of these. In older versions of TWiki,
	* ==Set <nop>ALLOWWEBVIEW = <nop>==
meant the same as not setting it at all. However since TWiki Dakar release, it means _allow no-one access_ i.e. prevent anyone from viewing the web. Similarly
	* ==Set <nop>DENYWEBVIEW = <nop>==
now means _do not deny anyone the right to view this web_. See "How TWiki evaluates ALLOW/DENY settings" below for more on this.

---+++ Controlling access to a Topic

	* You can define these settings in the %WEBPREFSTOPIC% topic, preferable towards the end of the topic:
		* ==Set <nop>DENYTOPICVIEW = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWTOPICVIEW = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>DENYTOPICCHANGE = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWTOPICCHANGE = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>DENYTOPICRENAME = &lt; comma-delimited list of Users and Groups &gt;==
		* ==Set <nop>ALLOWTOPICRENAME = &lt; comma-delimited list of Users and Groups &gt;==

Remember when opening up access to specific topics within a restricted web that other topics in the web - for example, the WebLeftBar - may also be accessed when viewing the topics. The message you get when you are denied access should tell you what topic you were not permitted to access.

*Be careful* with empty values for any of these. In older versions of TWiki,
	* ==Set <nop>ALLOWTOPICVIEW = <nop>==
meant the same as not setting it at all. However since TWiki Dakar release, it means _allow no-one access_ i.e. prevent anyone from viewing the topic. Similarly
	* ==Set <nop>DENYTOPICVIEW = <nop>==
now means _do not deny anyone the right to view this topic_. See "How TWiki evaluates ALLOW/DENY settings" below for more on this.

---+++ Controlling access to Attachments

Attachments are referred to directly, and are not normally indirected via TWiki scripts. This means that the above instructions for access control will _not_ apply to attachments. It is possible that someone may inadvertently publicise a URL that they expected to be access-controlled.

The easiest way to apply the same access control rules for attachments as apply to topics is to use the Apache =mod_rewrite= module, and configure your webserver to redirect accesses to attachments to the TWiki =viewfile= script. For example,

<verbatim>
  ScriptAlias /twiki/bin/ /filesystem/path/to/twiki/bin/
  Alias /twiki/pub/		 /filesystem/path/to/twiki/pub/

  RewriteEngine on
  RewriteRule ^/twiki/pub/TWiki/(.*)$ /twiki/pub/TWiki/$1 [L,PT]
  RewriteRule ^/twiki/pub/([^\/]+)/([^\/]+)/([^\/]+)$ /twiki/bin/viewfile/$1/$2?filename=$3 [L,PT]
</verbatim>

That way all the controls that apply to the topic also apply to attachments to the topic. Other types of webserver have similar support.

__Note:__ Images embedded in topics will load much slower since each image will be delivered by the =viewfile= script.

---+++ How TWiki evaluates ALLOW/DENY settings

When deciding whether to grant access, TWiki evaluates the following rules in order (read from the top of the list; if the logic arrives at *PERMITTED* or *DENIED* that applies immediately and no more rules are applied). You need to read the rules bearing in mind that VIEW, CHANGE and RENAME access may be granted/denied separately.
	1 If the user is a [[#SuperAdminGroup][super-user]]
		* access is *PERMITTED*.
	1 If DENYTOPIC is set to a list of wikinames
		* people in the list will be *DENIED*.
	1 If DENYTOPIC is set to _empty_ ( i.e. <tt>Set DENYTOPIC =</tt> )
		* access is *PERMITTED* _i.e_ no-one is denied access to this topic
	1 If ALLOWTOPIC is set
		1 people in the list are *PERMITTED*
		1 everyone else is *DENIED*
			* Note that this means that setting ALLOWTOPIC to empty _denies access to everyone except admins_ (unless DENYTOPIC is also set to empty, as described above)
	1 If DENYWEB is set to a list of wikiname
		* people in the list are *DENIED* access
	1 If ALLOWWEB is set to a list of wikinames
		* people in the list will be *PERMITTED*
		* everyone else will be *DENIED*
			* Note that setting ALLOWWEB to empty _denies access to everyone except admins_
	1 If you got this far, access is *PERMITTED*

---++ Access Control quick recipes

---+++ Obfusticating Webs

Another way of hiding webs is to keep them hidden by not publishing the URL and by preventing the ==all webs== search option from accessing obfuscated webs. Do so by enabling the ==NOSEARCHALL== variable in %WEBPREFSTOPIC%:
	* ==Set <nop>NOSEARCHALL = on==

This setup can be useful to hide a new web until content its ready for deployment, or to hide view access restricted webs.

__%X% Note:__ Obfuscating a web without view access control is very insecure, as anyone who knows the URL can access the web.

---+++ Authenticate all Webs and Restrict Selected Webs

Use the following setup to authenticate users for topic viewing in all webs and to restrict access to selected webs. Requires TWikiUserAuthentication to be enabled.

	1. *Restrict* view access to selected Users and Groups. Set one or both of these variables in its %WEBPREFSTOPIC% topic:
		* ==Set <nop>DENYWEBVIEW = &lt; list of Users and Groups &gt;==
		* ==Set <nop>ALLOWWEBVIEW = &lt; list of Users and Groups &gt;==
		* __Note:__ =DENYWEBVIEW= is evaluated before =ALLOWWEBVIEW=. Access is denied if the authenticated person is in the =DENYWEBVIEW= list, or not in the =ALLOWWEBVIEW= list. Access is granted in case =DENYWEBVIEW= and =ALLOWWEBVIEW= is not defined.
	1. *Hide* the web from an "all webs" search. Enable this restriction with the ==NOSEARCHALL== variable in its %WEBPREFSTOPIC% topic:
		* ==Set <nop>NOSEARCHALL = on==

---+++ Authenticate and Restrict Selected Webs Only

Use the following setup to provide unrestricted viewing access to open webs, with authentication only on selected webs. Requires TWikiUserAuthentication to be enabled.

	1. *Restrict* view access to selected Users and Groups. Set one or both of these variables in its %WEBPREFSTOPIC% topic:
		* ==Set <nop>DENYWEBVIEW = &lt; list of Users and Groups &gt;==
		* ==Set <nop>ALLOWWEBVIEW = &lt; list of Users and Groups &gt;==
		* __Note:__ =DENYWEBVIEW= is evaluated before =ALLOWWEBVIEW=. Access is denied if the authenticated person is in the =DENYWEBVIEW= list, or not in the =ALLOWWEBVIEW= list. Access is granted in case =DENYWEBVIEW= and =ALLOWWEBVIEW= is not defined.
	1. *Hide* the web from an "all webs" search. Enable this restriction with the ==NOSEARCHALL== variable in its %WEBPREFSTOPIC% topic:
		* ==Set <nop>NOSEARCHALL = on==

---+++ Hide Control Settings

__%T% Tip:__ To hide access control settings from normal browser viewing, place them in HTML comment markers.

<blockquote>
==&lt;!--== <br />
==&nbsp;  * Set <nop>DENYTOPICCHANGE = %MAINWEB%.<nop>SomeGroup== <br />
==--&gt;==
</blockquote>

%STOPINCLUDE%

__Related Topics:__ AdminDocumentationCategory
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