r21 - 27 Mar 2005 - 08:14:15 - TWikiContributorYou are here: NTL >  TWiki Web  > TWikiUserAuthentication

TWiki User Authentication

TWiki site access control and user activity tracking options

Overview

Authentication, or "login", is the process by which a user lets TWiki know who they are.

Authentication isn't just to do with access control. TWiki uses authentication to identify users, so it can keep track of who made changes, and manage a wide range of personal settings. With authentication enabled, users can personalise TWiki and contribute as recognised individuals, instead of shadows.

TWiki authentication is very flexible, and can either stand alone or integrate with existing authentication schemes. You can set up TWiki to require authentication for every access, or only for changes. Authentication is also essential for access control.

Quick Authentication Test - Use the %WIKIUSERNAME% variable to return your current identity:

TWiki user authentication is split into three sections; password management, user registration, and login management. Password management deals with how users are recognised (authenticated). Registration deals with how new users are added to the wiki. Login management deals with how users log in.

Once a user is logged on, they are remembered using a "session id" stored in a cookie in the browser (or by other less elegant means if the user has disabled cookies). This avoids them having to log on again and again.

Please note FileAttachments are not protected by TWiki User Authentication.

TIP Tip: TWiki:TWiki.TWikiUserAuthenticationSupplement on TWiki.org has supplemental documentation on user authentication.

Password Management

As shipped, TWiki supports the Apache 'htpasswd' password manager. This manager supports the use of .htpasswd files on the server. These files can be unique to TWiki, or can be shared with other applications (such as an Apache webserver). A variety of password encodings are supported for flexibility when re-using existing files. See the descriptive comments in the Security Settings section of the configure interface for more details.

New User Registration

New user registration uses the password manager to set and change passwords. It is also responsible for the new user verification process. the registration process supports single user registration via the TWikiRegistration page, and bulk user registration via the BulkRegistration page (for admins only).

The registration process is responsible for creating user topics.

Login Management

Login management controls the way users have to log in. There are three basic options; no login, login via a TWiki login page, and login using the webserver authentication support.

You can select your chosen login through the Security Settings pane in the configure interface.

No Login

Does exactly what it says on the tin. Forget about authentication to make your site completely public - anyone can browse and edit freely, in classic Wiki style. All visitors are given the TWikiGuest default identity, so you can't track individual user activity.

ALERT! Note: This setup is not recommended on public websites for security reasons; anyone would be able to change system settings and perform tasks usually restricted to the TWikiAdminGroup.

Template Login

Template Login asks for a username and password in a web page, and processes them using whatever Password Manager you choose. Users can log in and log out.

Enabling Template Login

  1. Use the configure interface to
    1. enable the TemplateLogin login manager (on the Security Settings pane).
    2. select the appropriate password manager for your system, or provide your own.
  2. Register yourself in the TWikiRegistration topic.
    HELP Check that the password manager recongises the new user. If you are using .htpasswd files, check that a new line with the username and encrypted password is added to the .htpasswd file. If not, you probably got a path wrong, or the permissions may not allow the webserver user to write to that file.
  3. Create a new topic to check if authentication works.
  4. Edit the TWikiAdminGroup topic in the Main web to include users with system administrator status.
    ALERT! This is a very important step, as users in this group can access all topics, independent of TWiki access controls.

TWikiAccessControl has more information on setting up access controls.

ALERT! At this time TWikiAccessControls cannot control access to files in the pub area, unless they are only accessed through the viewfile script. If your pub directory is set up in the webserver to allow open access you may want to add .htaccess files in there to restrict access.

TIP You can create a custom version of the TWikiRegistration form by deleting or adding input tags. The name="" parameter of the input tags must start with: "Twk0..." (if this is an optional entry), or "Twk1..." (if this is a required entry). This ensures that the fields are carried over into the user home page correctly.

TIP You can customize the default user home page in NewUserTemplate. The same variables get expanded as in the template topics

Apache Login

Using this method TWiki does not authenticate users internally. Instead it depends on the REMOTE_USER environment variable, which is set when you enable authentication in the webserver.

The advantage of this scheme is that if you have an existing website authentication scheme using Apache modules such as mod_auth_ldap or mod_auth_mysql you can just plug in directly to them.

The disadvantage is that because the user identity is cached in the browser, you can log in, but you can't log out again unless you restart the browser.

TWiki maps the REMOTE_USER that was used to log in to the webserver to a WikiName using the table in TWikiUsers. This table is updated whenever a user registers, so users can choose not to register (in which case their webserver login name is used for their signature) or register (in which case that login name is mapped to their WikiName).

The same private .htpasswd file used in TWiki Template Login can be used to authenticate Apache users, using the Apache Basic Authentication support. This allows the TWiki registration support to maintain usernames and passwords.

Enabling Apache Login using =mod_auth

You can use any other Apache authentication module that sets REMOTE_USER.
  1. Use configure to select the ApacheLogin login manager.
  2. Use configure to set up TWiki to create the right kind of .htpasswd entries.
  3. Create a .htaccess file in the twiki/bin directory.
    HELP There is an template for this file in twiki/bin/.htaccess.txt that you can copy and change. The comments in the file explain what need to be done.
    HELP If you got it right, the browser should now ask for login name and password when you click on the Edit. If .htaccess does not have the desired effect, you may need to "AllowOverride All" for the directory in httpd.conf (if you have root access; otherwise, e-mail web server support)
    ALERT! At this time TWikiAccessControls do not control access to files in the pub area, unless they are only accessed through the viewfile script. If your pub directory is set up to allow open access you may want to add .htaccess files in there as well to restrict access
  4. You can create a custom version of TWikiRegistration by deleting or adding input tags. The name="" parameter of the input tags must start with: "Twk0..." (if this is an optional entry), or "Twk1..." (if this is a required entry). This ensures that the fields are carried over into the user home page correctly.
    You can customize the default user home page in NewUserTemplate. The same variables get expanded as in the template topics
  5. Register yourself in the TWikiRegistration topic.
    HELP Check that a new line with the username and encrypted password is added to the .htpasswd file. If not, you may have got a path wrong, or the permissions may not allow the webserver user to write to that file.
  6. Create a new topic to check if authentication works.
  7. Edit the TWikiAdminGroup topic in the Main web to include users with system administrator status.
    ALERT! This is a very important step, as users in this group can access all topics, independent of TWiki access controls.
TWikiAccessControl has more information on setting up access controls.

Logons via bin/logon

Any time a user enters a page that needs authentication, they will be forced to log on. It may be convenient to have a "logon" as well, to give the system a chance to identify the user and retrieve their personal settings. It may be convenient to force them to log on.

The bin/logon script accomplishes this. The bin/logon script must be setup in the bin/.htaccess file to be a script which requires a valid user. However, once authenticated, it will simply redirect the user to the view URL for the page from which the logon script was linked.

Sessions

TWiki uses the CPAN:CGI::Session and CPAN:CGI::Cookie modules to track sessions using cookies. These modules are de facto standards for session management among Perl programmers. If you can't use Cookies for any reason, CPAN:CGI::Session also supports session tracking using the client IP address. See How to choose an authentication method for a discussion of the pros and cons of the various authentication methods.

There are a number of TWikiVariables available that you can use to interrogate your current session. You can even add your own session variables to the TWiki cookie. Session variables are referred to as "sticky" variables.

Getting, Setting, and Clearing Session Variables

You can get, set, and clear session variables from within TWiki web pages or by using script parameters. This allows you to use the session as a personal "persistent memory space" that is not lost until the web browser is closed. Also note that if a session variable has the same name as a TWiki preference, the session variables value takes precedence over the TWiki preference. This allows for per-session preferences.

To make use of these features, use the tags:

%SESSION_VARIABLE{ "varName" }%
%SESSION_VARIABLE{ "varName" set="varValue" }%
%SESSION_VARIABLE{ "varName" clear="" }%

Cookies and Transparent Session IDs

TWiki normally uses cookies to store session information on a client computer. Cookies are a common way to pass session information from client to server. TWiki cookies simply hold a unique session identifier that is used to look up a database of session information on the TWiki server.

For a number of reasons, it may not be possible to use cookies. In this case, TWiki has a fallback mechanism; it will automatically rewrite every internal URL it sees on pages being generated to one that also passes session information.

TWiki Username vs. Login Username

This section applies only if you are using authentication with existing login names (i.e. mapping from login names to WikiNames).

NTL internally manages two usernames: Login Username and TWiki Username.

  • Login Username: When you login to the intranet, you use your existing login username, ex: pthoeny. This name is normally passed to TWiki by the REMOTE_USER environment variable, and used internally. Login Usernames are maintained by your system administrator.

  • TWiki Username: Your name in WikiNotation, ex: PeterThoeny, is recorded when you register using TWikiRegistration; doing so also generates a personal home page in the Main web.

TWiki can automatically map an Intranet (Login) Username to a TWiki Username if the {AllowLoginName} is enabled in configure. The default is to use your WikiName as a login name.

NOTE: To correctly enter a WikiName - your own or someone else's - be sure to include the Main web name in front of the Wiki username, followed by a period, and no spaces, for example Main.WikiUsername or %MAINWEB%.WikiUsername. This points WikiUsername to the Main web, where user home pages are located, no matter which web it's entered in. Without the web prefix, the name appears as a NewTopic? everywhere but in the Main web.

Changing Passwords

If your {PasswordManager} supports password changing, you can change and reset passwords using forms on regular pages.

Changing E-mail Addresses

If the active {PasswordManager} supports storage and retrieval of user e-mail addresses, you can change your e-mail using a regular page. As shipped, this is true only for the Apache 'htpasswd' password manager.

Controlling access to individual scripts

You may want to add or remove scripts from the list of scripts that require authentication. The method for doing this is different for each of Template Login and Apache Login.
  • For Template Login, update the {AuthScripts} list using configure
  • For Apache Login, add/remove the script from .htaccess

How to choose an authentication method

One of the key features of TWiki is that it is possible to add HTML to topics. No authentication method is 100% secure on a website where end users can add HTML, as there is always a risk that a malicious user can add code to a topic that gathers user information, such as session IDs. The TWiki developers have been forced to make certain tradeoffs, in the pursuit of efficiency, that may be exploited by a hacker.

This section discusses some of the known risks. You can be sure that any potential hackers have read this section as well!

Firstly, the most secure method is without doubt to use the webserver authentication support, with Sessions turned off.

The second most secure method is to use TWiki's internal authentication with Sessions turned off. This method is less secure than using the webserver because passwords are sent in plain text and can therefore be intercepted in transit.

As soon as you allow the server to maintain information about a logged-in user, you open a door to potential attacks. There are a variety of ways a malicious user can pervert TWiki to obtain another users session ID, the most common of which is known as a cross-site scripting attack. Once a hacker has an SID they can pretend to be that user.

To help prevent these sorts of attacks, TWiki supports IP matching, which ensures that the IP address of the user requesting a specific session is the same as the IP address of the user who created the session. This works well as long as IP addresses are unique to each client, and as long as the IP address of the client can't be faked.

The third most secure method is to use sessions with IP matching ({UseIPMatching} switched on). Shorter session expiry times are more secure ({Sessions}{ExpireAfter}). The default session lifetime is 6 hours, which is quite a long lifetime for a session.

Session IDs are usually stored by TWiki in cookies, which are stored in the client browser. Cookies work well, but not all environments or users permit cookies to be stored in browsers. So TWiki also supports two other methods of determining the session ID. The first method uses the client IP address to determine the session ID. The second uses a rewriting method that rewrites local URLs in TWiki pages to include the session ID in the URL.

The first method works well as long as IP addresses are unique to each individual client, and client IP addresses can't be faked by a hacker. If IP addresses are unique and can't be faked, it is almost as secure as cookies + IP matching, so it ranks as the fourth most secure method.

If you have to turn IP matching off, and cookies can't be relied on, then you may have to rely on the second method, URL rewriting. This method exposes the session IDs very publicly, so should be regarded as the least secure method.

See TWiki:TWiki.SecuringTWikiSite for more information.

Related Topics: AdminDocumentationCategory, TWikiAccessControl, TWiki:TWiki.TWikiUserAuthenticationSupplement, TWiki:TWiki.SecuringTWikiSite

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

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