Daya Bay Reactor Neutrino Experiment TWiki > TWikiAccessControl Daya Bay webs:
Public | 中文 | Internal | Help

Log In or Register

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

Your organization will learn that, while fostering an open collaborative environment, soft security (peer review), together with version control (complete audit trail) will take care of any security concern you might have.

Open, free-form editing is the essence of WikiCulture - what makes TWiki different and often more effective than other collaborative environments. 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 Public on       DybAdminGroup, DavidJaffe, TWikiRegistrationAgent   DybAdminGroup
Preferences Home TWiki on       TWikiAdminGroup   TWikiAdminGroup
Preferences Home Main on       DybAdminGroup, TWikiRegistrationAgent   DybAdminGroup
Preferences Home Public.Chinese on       DybAdminGroup, DavidJaffe, TWikiRegistrationAgent   DybAdminGroup
Preferences Home Public.Public on       DybAdminGroup, DavidJaffe, TWikiRegistrationAgent   DybAdminGroup
Preferences Home Public.Public.Chinese on       DybAdminGroup, DavidJaffe, TWikiRegistrationAgent   DybAdminGroup
Preferences Home Sandbox on            
Preferences Home Sandbox.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 Public 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 Daya Bay 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 Public, 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:

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

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

Allowing public access to specific topics in a restricted web

You may want to completely open up access to a specific topic within a restricted web - allowing access by anybody. There is a special group for that - Public.AllUsersGroup. The following setting allows view access to the topic by anybody even if they are not authenticated.

Alternatively, you can grant access only to authenticated users by Public.AllAuthUsersGroup. If an unauthenticated user accesses a topic having the following setting, they are asked to authenticate themself.

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.

As mentioned in the following section, meaning of an empty value set to DENYTOPICVIEW, DENYTOPICCHANGE, and DENYTOPICRENAME has been changed in TWiki 6.0. To keep those TWiki topics having empty DENYTOPICOPERAION accessible by everybody, those need to be replaced with

For that, tools/eliminate_emptydenytopic is provided. After upgrading from pre 6.0 to post 6.0, you need to run it.

Empty values in access control variables

Setting an empty value to an access control variable is the same as not setting at all:

ALERT! Since TWiki 4.0 and prior to TWiki 6.0 setting DENYTOPICVIEW, DENYTOPICCHANGE, or DENYTOPICRENAME to an empty value meant "do not deny anyone regardless of the corresponding ALLOWTOPICX", which is no longer the case. Back then, setting an empty value to DENYTOPICX was the only way to open up a topic to everybody in a restricted web. Now that we have AllUsersGroup and AllAuthUsersGroup, there is no need for that behaviour, which caused a lot of confusion and debate.

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
  2. If DENYTOPIC is set to a list of wikinames
  3. If DENYTOPIC is set to empty ( i.e. Set DENYTOPIC = )
  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
  6. If ALLOWWEB is set to a list of wikinames
  7. If you got this far, access is PERMITTED

Allowing web creation by user mapping manager

There are cases where DENYROOTCHANGE, ALLOWROOTCHANGE, DENYWEBCHANGE, and ALLOWWEBCHANGE, and DENYWEBCHANGE are not capable enough to implement web creation permission you want. To cope with such cases, when a new web is created, the canCreateWeb($cUID, $web) method of the user mapping manager is called if the method exists. If it returns true, TWiki goes ahead and create the web without checking access control variables. Please read AllowWebCreateByUserMappingManager for more details.

User masquerading

There are cases where it's handy to access TWiki on behalf of somebody else retaining a trace of your real identity rather than completely becoming a different user. We call it user masquerading. TWiki provides a framework to implement that. Please read UserMasquerading for more information.

This is an advanced feature and not many TWiki sites are using, but there is a part in the following section mentioning it, it's mentioned here.

Dynamic access control

There are pitfalls and you need to harden your web to avoid unexpected access. Before using this feature, please read this entire section through carefully.

You may want to restrict access dynamically -- based on topic name, a form field value, or some combination of factors. To cope with such situations, the dynamic access control mechanism is provided. If you set DYNAMIC_ACCESS_CONTROL 'on' at WebPreferences of the web, TWiki variables in access control variables mentioned above are expanded.

Example 1 - restriction based on topic name

Let's assume you need to restrict changes only to the CroniesGroup members except with topics whose name ends with Public, which need be changed by anybody. That is achieve by the following settings on WebPrefences.

   * Set DYNAMIC_ACCESS_CONTROL = on
   * Set ALLOWWEBCHANGE = %IF{"'%CALCULATE{$SUBSTRING(%TOPIC%, -6, 6)}%' = 'Public'" then="%WIKINAME%" else="CroniesGroup"}%

Example 2 - restriction based on form field

Let's assume:

That is achieve by the following settings on WebPreferences.

   * Set DYNAMIC_ACCESS_CONTROL = on
   * Set ALLOWWEBVIEW = %IF{"'%CALCULATE{$SUBSTRING(%TOPIC%, 1, 6)}%' = 'ReqEnt' and '%FORMFIELD{Requestor}%' != '%WIKINAME%'" then="SupportGroup" else="%WIKINAME%"}%

Specifically the following access control variables are subject to TWiki variable expansion in their values.

DENYROOT* and ALLOWROOT* are not subject to variable expansion. Because there has been no good use cases presented.

Dynamic access control in accessing a different web's topic

Let's assume WebA has the following lines on WebPreferences.

   * Set DYNAMIC_ACCESS_CONTROL = on
   * Set MEMBERS = JaneSmith, JoeSchmoe
   * Set ALLOWWEBVIEW = %MEMBERS%
This is not a good way to use dynamic access control but it does restrict access only to those listed in MEMBERS. However, access control doesn't work as expected when WebA.TopicB is accessed from WebC.TopicD by %INCLUDE{WebA.TopicB}% or other variables. This is because %MEMBERS% is defined in WebA and may have a different value in other webs.

You may think the following lines cheat the access control on WebA but actually not.

   * Set MEMBERS = %WIKINAME%
%INCLUDE{WebA.TopicB}%
This is because when a topic (e.g. WebC.TopicD) is accessed from browser and the topic refers to another topic in a different web (e.g. WebA.TopicB) and the different web employs dynamic access control, access to another topic is defined being on the safer side.

Topic level dynamic access control

On a topic, it's possible to use a variable defined on the topic for topic level access restriction. E.g.

   * Set MEMBERS = JaneSmith, JoeSchmoe
   * Set ALLOWTOPICVIEW = %MEMBERS%
[This is not a good way to use dynamic access control

Dynamic access control and user masquerading

Your user mapping handler may be providing the UserMasquerading feature. In that case, you expect dynamic access control to just work when user masquerading is in effect. Otherwise, you cannot test if your dynamic access control configuration is working as expected on your own.

Dynamic access control does work as expected even if user masquerading is in effect. For that, the following things are happening under the hood.

Let's think about Example 2 mentioned above. When you masquerading as SomebodyElse, you need to be able to see SomebodyElse's requests only. In the access control setting, a form field value is compared with %WIKINAME%. While user masquerading is in effect, your wiki name is YourNameOnBehalfOfSomebodyElse. It cannot match the form field value.

To make dynamic access control work under these circumstances, variable expansion for dynamic access control is skewed as follows. Specifically, the following variables are expanded to the value of SomeboyElse's rather than YourNameOnBehalfOfSomebodyElse's.

Avoiding vulnerability

By default, user level preferences are read before web level preferences. This means a user can set a preferences variable at the user level and finalise it. To prevent this sort of attack, you need to harden your web or site by disabling user preferences by e.g. having the following line on lib/LocalSite.cfg

$TWiki::cfg{DemoteUserPreferences}= 1;
and having the following line on your WebPreferences and then finalise DENYUSERPREFEENCES.
   * Set DENYUSERPREFEENCES = all
Please read TWikiVariables#ControllingUserLevelPrefsOverride for details.

Again by default, predefined variables such as %IF{...}% can be overridden by preferences variables. If user preferences are disabled, ordinary users cannot attack using user preferences, but topic level preferences may cause unexpected consequences. As such, all predefined variables need to be made un-overridable by having the following line on WebPreferences and then finalise OVERRIDABLEPREDEFINEDVARIABLES.

   * Set OVERRIDABLEPREDEFINEDVARIABLES =
Please read TWikiVariables#PredefinedVariables for details.

Disabling dynamic access control

You may not be comfortable with dynamic access control because it may slow things down. Or you may not want to be bothered by questions raised by users about it. If so, you can disable it by setting DYNAMIC_ACCESS_CONTROL 'off' and then finalizing at the local site level. (cf. TWikiVariables#Setting_Preferences_Variables)

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

Customizing "access denied" message

When access is denied, a page as follows is displayed:

access-denied.png

You may want to customize the passage annotated in the red rectangle. For example, with a web restricting access, you may want to show the link to an access request form.

You can achieve that by setting TOPIC_ACCESS_CONTACT varialbe on WebPreferences. e.g.

   * Set TOPIC_ACCESS_CONTACT = If you need to access this site, please apply [[Main.AccessForm][here]]
Please note that setting it on a topic other than WebPreferences does not take effect. This is a limitation of the current implementation.

Custom user/group notations

You can have custom user/group notations such as USER:userid and LDAPGROUP:group-name and use them for access control. For example:

   * Set ALLOWWEBCHANGE = UID:buzz, LDAPGROUP:foo-bar
In a large organization, TWiki may need to depend on user and group data provided by its infrastructure. Custom user/group notations are handy in such situations though it's not trivial to implement. Please read here for details.

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:

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 = Public.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.

Configuring access control for topics of a certain name in all webs

You may need to restrict access to topics of a certain name in all webs. For example, there might be an add-on refering to a certain topic of all webs. And the add-on does things only administrators are supposed to do. In that case, change to the topic needs to be restricted only to administrators and must not be overridable.

Let's say there is AutomationAddOn which refers to WebAutomation of all webs. And WebAutomation needs to be modifable only by administrators. That can be achieved by the following configuration.

$TWiki::cfg{Access}{Topic}{WebAutomation} = {
    DENYCHANGE => 'Main.AllUsersGroup',
};

In addition to ALLOWCHANGE, you can sepcify DENYCHANGE, ALLOWVIEW, DENYVIEW, ALLOWRENAME, and DENYRENAME as follows.

$TWiki::cfg{Access}{Topic}{SpecialTopic} = {
    DENYVIEW  => 'JoeSchmoe',
    ALLOWVIEW => 'FooGroup',
};

$TWiki::cfg{Access}{Topic}{TOPICNAME} has precedence over DENYTOPIC* and ALLOWTOPIC*. For example, if the configuration for WebAutomation is there as above, there is no way to allow non-adminsitrators to change the WebAutomation topic of any web.

As a way to configure access control, this may look crude. The reason why configured this way is that this can be part of plugin/add-on/contrib's configuration. For example, Config.spec of AutomationAddOn would have the following lines, with which proper access control to WebAutomation topics is implemented without the administrator knowing it.

$TWiki::cfg{Access}{Topic}{WebAutomation} = {
    DENYCHANGE => 'Main.AllUsersGroup',
};

Related Topics: AdminDocumentationCategory, TWikiUserAuthentication, AllowWebCreateByUserMappingManager, UserMasquerading, CustomUserGroupNotations, TWiki:TWiki.TWikiAccessControlSupplement

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



Revision: r42 - 2014-07-04 - 08:02:09 - TWikiContributor

Copyright © 1999-2018 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding Daya Bay? Send feedback
Note: Please contribute updates to this topic on TWiki.org at TWiki:TWiki.TWikiAccessControl.