IMPORTANT NOTE: Think twice before restricting read or write access to a web or a topic, because an open system where everybody can contribute is the essence of the WikiCulture. Experience shows that unrestricted write access works very well because:

• There is enough peer pressure to post only conform content.
• Content does not get lost because topics are under revision control.
• A topic revision can be undone by a member of the TWikiAdminGroup in case needed.

Users and Groups

Access control is based on users and groups.

Users are defined by the user topics in the Main web, i.e. TWikiGuest

• Users can be authenticated using basic authentication or SSL. Installation Notes has more.

Groups are defined by group topics in the Main web, i.e. TWikiAdminGroup

• A group topic name must end in ...Group
• The group topic should define these two variables:
  • Set GROUP = < list of users and groups >
  • Set ALLOWTOPICCHANGE = < list of users and groups >
• GROUP defines the members of the group; it is a comma delimited list of users and other groups. Example:
      * 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, i.e.
      * Set ALLOWTOPICCHANGE = Main.TWikiAdminGroup
  for the TWikiAdminGroup topic. (This is to prevent users not in the group from editing the topic and gaining unauthorized membership to the group.)

Write Access Restriction for Individual Topics

You can define restrictions of who is allowed to make changes to a topic or attach files to it.

Define one or both of these variables in a topic, preferably at the end of the topic:

• 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.

Write Access Restriction for a Whole TWiki Web

You can define restrictions of who is allowed to make changes to a TWiki web. This includes 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 like the one for Access Control for Individual Topics; with these additions:

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

Read Access Restriction for a Whole TWiki Web

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

Define one or both of these variable in the WebPreferences topic:

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

Notes for read access restriction:

• Read access restriction only works if the view script is authenticated, that means that users need to log on also just to read topics. TWiki Installation has more on basic authentication based on the .htaccess file.
• There is a workaround if you prefer to to have unrestricted access to view topics located in normal webs, and to authenticate users only for webs where view restriction is enabled:
  • Leave the view script non authenticated in the .htaccess file.
  • Enable the $doRememberRemoteUser flag in wikicfg.pm as described in TWiki Authentication. TWiki will now remember the IP address of an authenticated user.
  • Copy the view script to viewauth (or better, create a symbolic link)
  • Enable authentication for the viewauth script in the .htaccess file.
  • When a user accesses a web where you enabled view restriction, TWiki will redirect from the view script to the viewauth script once (this hapens 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.
• The view restriction is not suitable for very sensitive content since there is a way to circumvent the read access restriction.

Related topics: TWikiPreferences, WebPreferences (in every web), TWikiAdminGroup, TWikiGroups

-- PeterThoeny - 20 Jan 2001