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TWiki User Authentication

TWiki site access control and user activity tracking options

Overview

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

Authentication isn't just about 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 ghosts.

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 %USERINFO% variable to return your current identity:

• You are guest, TWikiGuest,

TWiki user authentication is split into four categories: Password management, user mapping, user registration, and login management. Password management deals with how users' personal data is stored. Registration deals with how new users are added to the wiki. Login management deals with how users log in.

Once a user is logged in, they can be remembered using a Client Session stored in a cookie in the browser (or by other less elegant means if the user has cookies disabled). This avoids the need of having to log in again and again.

TWiki user authentication is configured through the Security Settings pane in the configure interface.

Please note that FileAttachments are not protected by TWiki user authentication by default. The TWiki:TWiki.ApacheConfigGenerator has an option to protect file attachments.

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.

You can easily plug in alternate password management modules to support interfaces to other third-party authentication databases.

User Mapping

Often, when you are using an external authentication method, you want to map from an unfriendly "login name" to a more friendly WikiName. Also, an external authentication database may well have user information you want to import into TWiki, such as user groups.

By default, TWiki supports mapping of usernames to wikinames, and supports TWiki groups internal to TWiki. If you want, you can plug in an alternate user mapping module to support importing groups and other entities.

User Registration

New user registration uses the password manager to set and change passwords, and to store email addresses. 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 also responsible for creating user topics and setting up the mapping information used by the User Mapping support.

Note: If you are restricting the entire Public web to TWikiGuest, you are required to add TWikiRegistrationAgent to ALLOWWEBCHANGE in your Public/WebPreferences. By doing so, new users are able to register without any errors.

Login Management

Login management controls how users log in. There are three basic options: No login, login via a TWiki login page, and login using webserver authentication support.

No Login (select none in configure)

No Login does exactly what it says. 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.

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 administrators.

Template Login (select TWiki::LoginManager::TemplateLogin in configure)

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. Client Sessions are used to remember users. Users can choose to have their session remembered so they will automatically be logged in the next time they start their browser.

Enabling Template Login

1. Use the configure interface to
   1. select the TWiki::LoginManager::TemplateLogin login manager (on the Security Settings pane).
   2. select the appropriate password manager for your system, or provide your own.
   3. there is also an EXPERT configure setting {TemplateLogin}{PreventBrowserRememberingPassword} that you can set to prevent browsers from remembering usernames and passwords if you are concerned about public terminal usage.
2. Register yourself in the TWikiRegistration topic.
   Check that the password manager recognises 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 Public web to include users with system administrator status.
   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.

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.

You can create a custom version of the TWikiRegistration form by copying the topic, and then deleting or adding input tags in your copy. 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 profile page correctly. Do not modify the version of TWikiRegistration shipped with TWiki, as your changes will be overwritten next time you upgrade.

The default new user template page is in TWiki.NewUserTemplate. The same variables get expanded as in the template topics. You can create a custom new user profile page by creating the Public.NewUserTemplate topic, which will then override the default.

Apache Login (select TWiki::LoginManager::ApacheLogin in configure)

Using this method TWiki does not authenticate users internally. Instead it depends on the REMOTE_USER environment variable, which the webserver passes to TWiki when you enable authentication in the webserver (as described in RFC 3875 - "The Common Gateway Interface v1.1" ).

The advantage of this scheme is that if you have an existing website authentication scheme using Apache modules, such as mod_authnz_ldap  or mod_authn_dbd , 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.

Warning: Do not use the Apache htpasswd program with .htpasswd files generated by TWiki! htpasswd wipes out email addresses that TWiki plants in the info fields of this file.

Enabling Apache Login using mod_auth

1. Use configure to select the TWiki::LoginManager::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.
   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 needs to be done.
   If you got it right, the browser should now ask for a login name and password when you click on 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)
   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 the TWikiRegistration form by copying the default topic, and then deleting or adding input tags in your copy. 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 profile page correctly. Do not modify the version of TWikiRegistration shipped with TWiki, as your changes will be overwritten next time you upgrade.
   The default new user template page is in TWiki.NewUserTemplate. The same variables get expanded as in the template topics. You can create a custom new user profile page by creating the Public.NewUserTemplate topic, which will then override the default.
5. Register yourself in the TWikiRegistration topic.
   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 Public web to include users with system administrator status.
   This is a very important step, as users in this group can access all topics, independent of TWiki access controls.

Logons via bin/logon

Any time a user requests a page that needs authentication, they will be forced to log on. It may be convenient to have a "login" link 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 in.

The bin/logon script enables this. If you are using Apache Login, the bin/logon script must be setup in the bin/.htaccess file to be a script which requires a valid user. Once authenticated, it will 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. 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.

You don't have to enable sessions to support logins in TWiki. However it is strongly recommended. TWiki needs some way to remember the fact that you logged in from a particular browser, and it uses sessions to do this. If you don't enable sessions, TWiki will try hard to remember you, but due to limitations in the browsers, it may also forget you (and then suddenly remember you again later!). So for the best user experience, you should enable sessions.

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 variables:

Special read-only session variables:

• %SESSION_VARIABLE{"AUTHUSER"}% - user ID, current value:
• %SESSION_VARIABLE{"SESSION_REQUEST_NUMBER"}% - number of pages accessed by current user since login, current value:

Notes:

• You cannot override access controls preferences this way.
• You can use the SetGetPlugin to set and get variables that are not user specific. This plugin can store variables persistently if needed.

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).

Daya Bay 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 user profile page in the Public 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 Public web name in front of the Wiki username, followed by a period, and no spaces, for example Public.WikiUsername or %USERSWEB%.WikiUsername. This points WikiUsername to the Public web, where user profile 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 Public web.

Changing Passwords

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

• The ChangePassword form ( TWiki/ChangePassword )
• The ResetPassword form ( TWiki/ResetPassword )

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.

• The ChangeEmailAddress form ( TWiki/ChangeEmailAddress )

Controlling access to individual scripts

• 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. 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!

At one extreme, the most secure method is to use TWiki via SSL (Secure Sockets Layer), with a login manager installed and Client Sessions turned off.

Using TWiki with sessions turned off is a pain, though, as with all the login managers there are occasions where TWiki will forget who you are. The best user experience is achieved with sessions turned on.

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.

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 "rather dodgy".

Most TWiki sites don't use SSL, so, as is the case with most sites that don't use SSL, there is always a possibility that a password could be picked out of the ether. Browsers do not encrypt passwords sent over non-SSL links, so using Apache Login is no more secure than Template Login.

Of the two shipped login managers, Apache Login is probably the most useful. It lets you do this sort of thing: wget --http-user=RogerRabbit --http-password=i'mnottelling http://www.example.com/bin/save/Sandbox/StuffAUTOINC0?text=hohoho,%20this%20is%20interesting i.e. pass in a user and password to a request from the command-line. However it doesn't let you log out.

Template Login degrades to url re-writing when you use a client like dillo that does not support cookies. However, you can log out and back in as a different user.

Finally, it would be really neat if someone was to work out how to use certificates to identify users.....

See TWiki:TWiki.SecuringTWikiSite for more information.

Related Topics: AdminDocumentationCategory, TWikiAccessControl, VarAUTHREALM, VarGET, VarLOGIN, VarLOGOUT, VarSESSIONID, VarSESSIONVAR, VarSESSIONVARIABLE, VarSET, TWiki:TWiki.TWikiUserAuthenticationSupplement, TWiki:TWiki.SecuringTWikiSite

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