The Caboteria / TWiki Web / TWikiAccessControl (11 Sep 2012, TWikiContributor)

TWiki Access Control

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

TWiki Access Control 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.

TIP Tip: TWiki:TWiki.TWikiAccessControlSupplement on TWiki.org has additional documentation on access control.

On this page:

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:

As a collaboration guideline:

Permissions settings of the webs on this TWiki site

Web Sitemap VIEW CHANGE RENAME
  Listed DENY ALLOW DENY ALLOW DENY ALLOW
Preferences Home Main on            
Preferences Home TWiki on       TWikiAdminGroup   TWikiAdminGroup
Preferences Home Sandbox on            

Please Note:

Note: Above table comes from SitePermissions

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:

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

Managing Groups

The following describes the standard TWiki support for groups. Your local TWiki may have an alternate group mapping manager installed. Check with your TWiki administrator if you are in doubt.

Groups are defined by group topics located in the Main web. To create a new group, visit TWikiGroups and enter the name of the new group ending in Group into the "new group" form field. This will create a new group topic with two important settings:

The GROUP setting is a comma-separated list of users and/or other groups. Example:

The ALLOWTOPICCHANGE setting 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 MarketingGroup topic write:

ALERT! Note: TWiki has strict formatting rules. Make sure you have a real bullet. (In raw edit it is three or six spaces, an asterisk, and an extra space in front of any access control rule.)

The Super Admin Group

A number of TWiki functions (for example, renaming webs) are only available to administrators. Administrators are simply users who belong to the SuperAdminGroup. This is a standard user group, the name of which is defined by {SuperAdminGroup} setting in configure. The default name of this group is the TWikiAdminGroup. The system administrator may have chosen a different name for this group if your local TWiki uses an alternate group mapping manager but for simplicity we will use the default name TWikiAdminGroup in the rest of this topic.

You can create new administrators simply by adding them to the TWikiAdminGroup topic. For example,

A member of the Super Admin Group has unrestricted access throughout the TWiki, so only trusted staff should be added to this group.

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.

Note that there is an important distinction between CHANGE access and RENAME access. A user can CHANGE a topic, but thanks to version control their changes cannot be lost (the history of the topic before the change is recorded). However if a topic or web is renamed, that history may be lost. Typically a site will only give RENAME access to administrators and content owners.

Controlling access to a Web

You can define restrictions on who is allowed to view a The Caboteria web. You can restrict access to certain webs to selected Users and Groups, by:

For example, set this to restrict a web to be viewable only by the MarketingGroup:

If your site allows hierarchical webs, then access to sub-webs is determined from the access controls of the parent web, plus the access controls in the sub-web. So, if the parent web has ALLOWWEBVIEW set, this will also apply to the subweb. Also note that you will need to ensure that the parent web's FINALPREFERENCES does not include the access control settings listed above. Otherwise you will not be able override the parent web's access control settings in sub-webs.

Creation and renaming of sub-webs is controlled by the WEBCHANGE setting on the parent web (or ROOTCHANGE for root webs). Renaming is additionally restricted by the setting of WEBRENAME in the web itself.

Note: If you restrict access to the Main, make sure to add the TWikiRegistrationAgent so that users can register. Example:

Note: For Web level access rights Setting any of these settings to an empty value has the same effect as not setting them at all. Please note that the documentation of TWiki 4.0 and earlier versions of TWiki 4.1 did not reflect the actual implementation, e.g. an empty ALLOWWEBVIEW does not prevent anyone from viewing the web, and an an empty DENYWEBVIEW does not allow all to view the web.

Controlling access to a Topic

For example, set this to restrict a topic to be viewable only by the MarketingExecGroup:

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.

The same rules apply to ALLOWTOPICCHANGE/DENYTOPICCHANGE and APPLYTOPICRENAME/DENYTOPICRENAME. Setting ALLOWTOPICCHANGE or ALLOWTOPICRENAME to en empty value means the same as not defining it. Setting DENYTOPICCHANGE or DENYTOPICRENAME to an empty value means that anyone can edit or rename the topic.

ALERT! If the same setting is defined multiple times the last one overrides the previous. They are not OR'ed together.

ALERT! The setting to an empty has caused confusion and great debate and it has been decided that the empty setting syntax will be replaced by something which is easier to understand in a later version of TWiki. A method to upgrade will be provided. Please read the release notes carefully when you upgrade.

See "How TWiki evaluates ALLOW/DENY settings" below for more on how ALLOW and DENY interacts.

Securing File Attachments

By default, TWiki does not secure file attachments. Without making the following changes to the twiki.conf file, it is possible for anyone who has access to the server to gain access to an attachment if they know the attachment's fully qualified path, even though access to the topic associated with the attachment is secured. This is because attachments are referred to directly by Apache, and are not by default delivered via TWiki scripts. This means that the above instructions for controlling to topics do not apply to attachments unless you make the changes as described below.

An effective way to secure attachments is to apply the same access control settings to attachments as those applied to topics. This security enhancement can be accomplished by instructing the webserver to redirect accesses to attachments via the TWiki viewfile script, which honors the TWiki access controls settings to topics. See the notes below for implications.

The preferred method to secure attachments is by editing the twiki.conf file to include: 

    ScriptAlias /do          /filesystem/path/to/twiki/bin
    Alias       /pub/TWiki   /filesystem/path/to/twiki/pub/TWiki
    Alias       /pub/Sandbox /filesystem/path/to/twiki/pub/Sandbox
    ScriptAlias /pub         /filesystem/path/to/twiki/bin/viewfile

Notes:

Controlling who can manage top-level webs

Top level webs are a special case, because they don't have a parent web with a WebPreferences. So there has to be a special control just for the root level.

Note that you do not require ROOTCHANGE access to rename an existing top-level web. You just need WEBCHANGE in the web itself.

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 an administrator
    • access is PERMITTED.
  2. If DENYTOPIC is set to a list of wikinames
    • people in the list will be DENIED.
  3. If DENYTOPIC is set to empty ( i.e. Set DENYTOPIC = )
    • access is PERMITTED i.e no-one is denied access to this topic.
      ALERT! Attention: Use this with caution. This is deprecated and will likely change in the next release.
  4. If ALLOWTOPIC is set
    1. people in the list are PERMITTED
    2. everyone else is DENIED
  5. If DENYWEB is set to a list of wikinames
    • people in the list are DENIED access
  6. If ALLOWWEB is set to a list of wikinames
    • people in the list will be PERMITTED
    • everyone else will be DENIED
  7. If you got this far, access is PERMITTED

Access control and INCLUDE

ALLOWTOPICVIEW and ALLOWTOPICCHANGE only applies to the topic in which the settings are defined. If a topic A includes another topic B, topic A does not inherit the access rights of the included topic B.

Examples: Topic A includes topic B

Access Control quick recipes

Restrict Access to Whole TWiki Site

In a firewalled TWiki, e.g. an intranet wiki or extranet wiki, you want to allow only invited people to access your TWiki. There are three options:

1. Install TWiki Behind Firewall:

The firewall takes care of giving access to TWiki to authorized people only. This is a typical setup for a company wiki. As for TWiki configuration, no special setup is needed.

2. Extranet TWiki Using Template Login:

All TWiki content (pages and attachments) need to be access controlled. The Template Login allows users to login and logout. Only logged in users can access TWiki content.

Configuration: Follow the default setup, then change these configure settings:

3. Extranet TWiki Using Apache Login:

All TWiki content (pages and attachments) need to be access controlled. The Apache Login does not offer a logout; typically the browser needs to be restarted to logout. Only logged in users can access TWiki content.

Configuration: Enable user authentication with ApacheLogin and lock down access to the whole twiki/bin and twiki/pub directories to all but valid users. In the Apache config file for TWiki (twiki.conf or .htaccess), replace the <FilesMatch "(attach|edit|... section with this: 

<FilesMatch ".*">
       require valid-user
</FilesMatch>

Notes:

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 WebPreferences topic:
    • Set DENYWEBVIEW = < list of Users and Groups >
    • Set ALLOWWEBVIEW = < list of Users and Groups >
    • 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 if DENYWEBVIEW and ALLOWWEBVIEW are not defined.

Hide Control Settings

TIP Tip: To hide access control settings from normal browser viewing, you can put them into the topic preference settings by clicking the link Edit topic preference settings under More topic actions menu. Preferences set in this manner are not visible in the topic text, but take effect nevertheless. Access control settings added as topic preference settings are stored in the topic meta data and they override settings defined in the topic text.

Alternatively, place them in HTML comment markers, but this exposes the access setting during ordinary editing.

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

Obfuscating 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 WebPreferences:

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

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

Read-only Skin Mode

It is possible to turn the PatternSkin and TopMenuSkin into read-only mode by removing the edit and attach controls (links and buttons). This is mainly useful if you have TWiki application pages or dashboards where you do not want regular users to change content. The read-only skin mode is not a replacement for access control; you can use it in addition to access control. Details at PatternSkinCustomization#ReadOnlySkinMode.

Related Topics: AdminDocumentationCategory, TWikiUserAuthentication, TWiki:TWiki.TWikiAccessControlSupplement

-- Contributors: TWiki:Main.PeterThoeny, TWiki:Main.MikeMannix, TWiki:Main.CrawfordCurrie

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