wiki:LdapPlugin

Version 30 (modified by germanbassi@…, 7 years ago) (diff)

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LDAP extensions

Abstract

LDAP support with group management has been added as a Trac extension. This extension enables to use existing LDAP groups to grant permissions rather than defining permissions for every single user on the system. The latest release also permits storage of permissions (both users and groups permissions) in the LDAP directory itself rather than in the SQL backend.

The original proposal for LDAP ACL is documented under ticket Trac#535 on the official web site.

This plugin follows the same license as Trac.

Requirements

This plugin works with Trac 0.10.
Although initial releases of the plugin (up to 0.2.2) have been written against Trac 0.9, they lack many of the latest plugin features and should be considered as experimental at best.

You need the Python LDAP module. It can be retrieved from python-ldap.
LdapPlugin has been tested on a Debian Linux Sarge/Sid (2.4.x and 2.6.x) server, a Windows XP SP2 workstation, as well as on MacBookPro OS 10.4.8, all of them running Python 2.4 with Trac 'development' releases.

To use the egg file you need to have setuptools, version 0.6+ installed.
Please refer to the TracPlugins page for information about plugin installation.

Important note

You need to grab a recent version of Trac from the trunk to make the Ldap permission store extension work as expected.
As the trunk API may vary without notice, the plugin may be broken if you run it with a different release.

Download

Installation

  • Build the egg file following the plugin packaging instructions
  • Copy the dist/LdapPlugin-0.y.z-py2.n.egg file in your plugins project directory.

Authentication

LdapPlugin does not perform authentication: Apache2 does, through the HTTP protocol, as with any other Trac installation.
LdapPlugin retrieves the groups to which the authenticated user belongs and checks the TracPermissions against these groups, along with the regular permissions for the user.

You probably want to use Apache2 LDAP authentication as well.
This topic is out of scope of this document but you may find useful information on the official Apache2 mod_ldap web site.

Apache 2.0

Here is an example of a typical LDAP section of an Apache2.0 configuration file:

<Location /trac/project>
   PythonOption TracEnv "/local/var/trac/project"
   PythonOption TracUriRoot "/trac/project"
   AuthType Basic
   AuthName "Project"
   Order Allow,Deny
   Allow from All
   AuthLDAPURL "ldap://localhost:389/dc=example,dc=org?uid"
   Require group cn=tracusers,dc=example,dc=org
</Location>

Apache 2.2

Since the mod_auth_ldap module has been superseded by the mod_authnz_ldap module for Apache 2.2, the configuration also needs a little tweaking. The above example would now look like:

<Location /trac/project>
   PythonOption TracEnv "/local/var/trac/project"
   PythonOption TracUriRoot "/trac/project"
   AuthType Basic
   AuthName "Project"
   AuthBasicProvider ldap
   Order Allow,Deny
   Allow from All
   AuthLDAPURL "ldap://localhost:389/dc=example,dc=org?uid"
   AuthzLDAPAuthoritative on
   Require ldap-group cn=tracusers,dc=example,dc=org
</Location>

Note that if you just use "Require valid-user" (to allow everybody with a valid LDAP login to access trac) you must set "AuthzLDAPAuthoritative off" according to the Apache documentation.

Configuration

You need to customize the trac.ini file of your project, then

  1. Optionally add the path to your plugin directory.
  2. Enable ldapplugin in [components] section, so that the Trac engine loads and uses this extension.
  3. Create a new section [ldap].
  4. Configure the LDAP directives to fit your LDAP server configuration.

To enable LdapPlugin you must add this line to the [components] section:

[components]
ldapplugin.* = enabled

The [ldap] section may contain the following options (which are presented down here with their default values)

[ldap]
# enable LDAP support for Trac
enable = false
# enable TLS support
use_tls = false
# LDAP directory host
host = localhost
# LDAP directory port (default port for LDAPS/TLS connections is 636)
port = 389
# BaseDN
basedn = dc=example,dc=com
# Relative DN for users (defaults to none)
user_rdn = 
# Relative DN for group of names (defaults to none)
group_rdn = 
# objectclass for groups
groupname = groupofnames
# dn entry in a groupname 
groupmember = member
# attribute name for a group
groupattr = cn
# attribute name for a user
uidattr = uid
# attribute name to store trac permission
permattr = tracperm
# filter to search for dn with 'permattr' attributes
permfilter = objectclass=*
# time, in seconds, before a cached entry is purged out of the local cache.
cache_ttl = 900
# maximum number of entries in the cache
cache_size = 100
# whether to perform an authenticated bind for group resolution
group_bind = false
# whether to perform an authenticated bind for permision store operations
store_bind = false
# user for authenticated connection to the LDAP directory
bind_user = 
# password for authenticated connection
bind_passwd =
# global permissions (vs. per-environment permissions)
global_perms = false
# group permissions are managed as addition/removal to the LDAP directory groups
manage_groups = true
# whether a group member contains the full dn or a simple uid
groupmemberisdn = true

You probably want to define at least enable=true and the basedn
The meaning of the options are pretty straightforward for LDAP administrators.

A typical setup for group resolution would look like this:

[ldap]
enable = true
basedn = dc=example,dc=org

A typical setup for all LDAP support (group resolution and permission store) would look like this:

[ldap]
enable = true
basedn = dc=example,dc=org
user_rdn = ou=people
group_rdn = ou=groups
store_bind = true
bind_user = cn=tracadmin,dc=example,dc=org
bind_passwd = mypasswd

Note about group_rdn and user_rdn

Starting from release v0.4.0, group_basedn and user_basedn options have been superseeded with group_rdn and user_rdn.
The new settings define the relative DNs respectively for the group and the user subtree, based on the common basedn trunk. For example:

  • ou=people,dc=example,dc=org would require the following settings:
    basedn = dc=example,dc=org
    user_rdn = ou=people
    
  • ou=groups,dc=example,dc=org would require the following settings:
    basedn = dc=example,dc=org
    group_rdn = ou=groups
    

Authenticated LDAP connections

If the server requires an authenticated connection to retrieve group permissions, you want to set group_bind = true in the [ldap] section and define the credentials as follows:

[ldap]
group_bind = true
bind_user = joeuser
bind_passwd = joepassword

If the server requires an authenticated connection to modify group permissions, you want to set store_bind = true in the [ldap] section and define the credentials as follows:

[ldap]
store_bind = true
bind_user = joeuser
bind_passwd = joepassword

Note: Most LDAP servers require authenticated bind to perform any kind of modifications. Anyway, it would be a bad idea to allow modifications from anybody.

Ldap permission store

If you wish to use the LDAP permission store feature, you need to tell Trac to use the LDAP extension rather than the internal default permission store which relies on the SQL backend.

Note that if you decide to store Trac permissions as a new LDAP attribute, you will need LDAP schema management rights. Furthermore, some LDAP servers (e.g. Active Directory) might not allow the deletion of attribute definitions.

To achieve this setting, add the following line to the main [trac] section of your trac.ini configuration file:

[trac]
# ...
permission_store = LdapPermissionStore

You also need to enable LdapPermissionStore for LdapPlugin by adding:

[components]
ldapplugin.* = enabled

The extension differentiates group permissions from user permission. This permits to use distinct objectclasses in the LDAP directory, to store permission. For example thanks to the groupattr and uidattr attributes, you can define group permission to LDAP entries such as

dn: cn=managers,dc=example,dc=org
objectclass: groupofnames
objectclass: trac
member: uid=chandler,dc=example,dc=org
member: uid=joey,dc=example,dc=org
tracperm: WIKI_ADMIN
tracperm: TICKET_ADMIN

and define user permission to LDAP entries such as

dn: uid=courtney,dc=example,dc=org
objectclass: user
objectclass: trac
tracperm: TICKET_VIEW
tracperm: REPORT_CREATE
tracperm: REPORT_VIEW

It is worth noting that the dn used for groups and for users may be different, which should make things easier to add TracPermissions into your existing LDAP directory.

To differentiate a group name from a user name in trac-admin, prefix the group name with the @ characters. This syntax has been borrowed from Samba and many other software dealing with group management.
One would grant the above permissions using the following trac-admin commands

permission add @managers WIKI_ADMIN
permission add @managers TICKET_ADMIN
permission add courtney TICKET_VIEW
permission add courtney REPORT_CREATE
permission add courtney REPORT_VIEW

Please note that the LDAP permission store never attemps to create a new entry in the LDAP directory. To grant (or revoke) permissions to/from the LDAP directory, the targetted LDAP entry should exist in the directory and the attribute defined by the permattr option should be writtable for the store_user user.

Please have a look at the LdapPluginTests page to get an overview of LDAP ACLs (access control lists) that manages LDAP operations on a directory.

Permissions

Once LDAP support has been activated, you can use trac-admin as usual to define TracPermissions.
However, you can now use the existing groups defined in your LDAP directory to assign permissions.

A LDAP group should start with the '@' character

Example:

Trac [/var/local/db/trac/public]> permission list

User             Action
-------------------------------
@administrators  TRAC_ADMIN
@betatesters     WIKI_CREATE
@betatesters     WIKI_MODIFY
eblot            TRAC_ADMIN
anonymous        BROWSER_VIEW
anonymous        CHANGESET_VIEW
anonymous        FILE_VIEW
anonymous        LOG_VIEW
anonymous        SEARCH_VIEW
anonymous        TIMELINE_VIEW
anonymous        WIKI_VIEW

Here, people who are declared in the 'administrator' LDAP group have the TRAC_ADMIN permission, and people who are declared in the 'betatesters' LDAP group have the WIKI_CREATE and WIKI_MODIFY permission.

You can obviously still use permissions for regular user such as eblot in the example above.

Note: Please remember that anonymous and authenticated are special users but are considered by the permission backend just like any other regular user.
This means that you need to add both these special users in your LDAP directory if you wish to assign permission to these joker entries. The directory configuration proposed in the test page may give you some hints about how to setup your LDAP directory.

Group of names

There are usually two flavours to manage group permissions in LDAP:

  1. The group contains a list of fully qualified dns
    dn: cn=fakedoctors,ou=groups,dc=example,dc=org
    cn: fakedoctors
    objectClass: groupOfNames
    objectClass: top
    member: uid=meredith,ou=groups,dc=example,dc=org
    member: uid=georges,ou=groups,dc=example,dc=org
    member: uid=izzie,ou=groups,dc=example,dc=org
    
    With such an environment, your [ldap] section would contain
    [ldap]
    ...
    group_rdn = ou=groups
    groupmemberisdn = true
    groupname = groupofnames
    groupmember = member
    
  2. The group contains a list of simple uids
    dn: cn=fakedoctors,ou=groups,dc=example,dc=org
    cn: fakedoctors
    objectClass: posixGroup
    objectClass: top
    memberUid: uid=meredith
    memberUid: uid=georges
    memberUid: uid=izzie
    
    With such an environment, your [ldap] section would contain
    [ldap]
    ...
    group_rdn = ou=groups
    groupmemberisdn = false
    groupname = posixgroup
    groupmember = memberUid
    

Beware, if you use this second scheme, you should have these lines in your apache configuration:

<Location /trac/project>
   ...
   AuthLDAPGroupAttribute memberUid
   AuthLDAPGroupAttributeIsDN off
   ...
</Location>

Global vs. Environment permissions

Starting from release v0.3.0, permissions are not defined globally (unless global_perms is set in the environment configuration file), but on per-environment basis.

With environment-wide permissions, it is now possible to define distinct permissions for each Trac environment (as long as their name differ) even if they access the same LDAP directory.

The Trac LDAP permission attribute value are prefixed with the environment name.
Using the previous example, assuming the environment name is named "test", permission attributes would become:

dn: uid=courtney,dc=example,dc=org
objectclass: user
objectclass: trac
tracperm: test:TICKET_VIEW
tracperm: test:REPORT_CREATE
tracperm: test:REPORT_VIEW

It is still possible to use global permissions by setting in the [ldap] section of the environment configuration file:

global_perms = true

When a directory contains global permission directives, those permissions apply on every Trac environment accessing the LDAP directory, whichever the global_perms value. However, permissions are always created using the current environment permission setting.

From the administrative point of view (trac-admin, WebAdmin, ...), there are no changes: permission are defined and retrieved as usual.

Note: The environment name is based on the root directory of the Trac environment. This means that if you use different environment with the same name, such as: /var/local/trac/test and /var/db/test, they are both named "test" and share the same permissions. This is a known limitation of the current implementation.

Group management

Starting from release v0.4.1, the LdapPlugin permission store offers two ways to store group membership:

  1. Permission-based management (default setting):
    In this configuration, the plugin mimics the original Trac membership management, but does not follow the LDAP way: group membership is defined as permission actions, which leads to manage permissions concurrently from the permission actions and the existing LDAP groups
  2. Ldap group management (recommended settings):
    In this configuration, the plugin only uses the LDAP groups to manage group membership. The plugin adds or removes group members from existing LDAP groups

Activation

The new group management scheme can be activated using the manage_groups option.

Example

The following permission command

permission add eblot @developers

would lead to a very modification in the LDAP directory

  1. The permission-based setting would add a tracperm attribute to the user entry
    # eblot, people, example.org
    dn: uid=eblot,ou=people,dc=example.org
    objectClass: tracuser
    tracperm: @developers
    ...
    
  2. The LDAP group setting would add a new member attribute to the group entry
    # developers, groups, example.org
    dn: cn=developers,ou=groups,dc=example.org
    objectClass: groupOfNames
    objectClass: tracgroup
    member: uid=eblot,ou=people,dc=example.org
    ...
    

Important notes

  1. The LDAP plugin is not able to create new groups or new users from scratch. Users and groups must already exist in the LDAP directory. It would be difficult to create a new LDAP group or a new LDAP user from Trac, as the creation of a LDAP resource usually requires properties which are not made available to the LDAP plugin.
    The above point means that the Trac administrator should probably creates the users and the groups from outside the Trac administration console (or WebAdmin). LdapPlugin is designed to integrate Trac with an existing LDAP directory, not to manage the directory.
  2. Default LDAP group policy usually requires that each group contains at least one member. If the administrator tries to remove the last member of a LDAP group, the LdapPlugin may refuse to perform this action (depending on the LDAP server setup).
  3. Note that LDAP group management only deals with explicit groups, i.e. any word that starts with a @ character. You can therefore mix aliases and LDAP directory groups:
    • permission add eblot devteam is a group alias, managed as any Trac permission
    • permission add devteam @developers is managed as a LDAP directory group (if manage_groups option is enabled)

Known limitations

  • Only LDAP v3 protocol is supported. This extension may work with v2 protocol as well, if the v3 specifier is removed from the code.

ToDo list

  • Add user detail support so that the full name and email address are retrieved from the LDAP server. It would require a new extension point in Trac engine, which might be called IUserDirectory (not before Trac 0.11 at best)
  • There's probably a lot of room for improvement (and debugging) ;-)

Testing

The LdapPluginTests page gives some hints about how to test the Ldap extension for Trac

History

  • v0.0: First attempt to write a LDAP bridge for Trac based on Trac 0.8, which required some hacks into the Trac engine.
  • v0.1: A new implementation has started on September, 1st '05, to profit from the new TracPlugins module architecture introduced in Trac 0.9-pre.
    This implementation should bring the following improvements:
    • includes a cache to dramatically reduce LDAP requests
    • better handling of LDAP errors
      This extension works with Trac 0.9-pre1 and requires the setuptools, version 0.5a13
  • v0.2: This new release fixes up a couple of bugs and works with Trac 0.9-pre2. It requires the setuptools, version 0.6+.
    It introduces support for LDAP permission store: TracPermissions can now be stored into the LDAP directory, rather than in the SQL backend.
    Each feature (LDAP as a provider of group permissions, LDAP as a permission store) are independent and can be enabled or disabled on demand.
  • v0.2.1: Bug fixing
  • v0.2.2: Introduce support for disting DN for users and groups (implemented suggestion described in #75)
  • v0.2.3: Update to support the new boolean parsing introduced in the official Trac trunk (requires Trac 0.10)
  • v0.3.0: Introduce per-environment permissions: permissions are defined to the current environment and do not overlap with other Trac environments using the same LDAP directory, unless the global_perms configuration parameters is set.
  • v0.4.0: Major rewrite of the LdapPlugin to support Trac trunk 3419, including better support for groups (user dns may be part of a different subtree than group dns, such as ou=people vs. ou=groups), improved cache management, as well as many bug fixes and code clean up.
  • v0.4.1: Introduce a new feature: group management is done as addition and removal to the LDAP groups of names: instead of storing groups as trac permissions (as the default permission store does), the plugin is not able to add and remove members to the LDAP group of names.
  • v0.4.2: Fix up an important issue with the management of the caches. The plugin has also been tested with the WebAdmin plugin.
  • v0.4.3: Fix up two issues with authentication (an invalid user identifier was sent to the LDAP server)
  • v0.4.4: Enable support for posix groups (and group members w/o distinguish name)
  • v0.5.0: Add basic support for LDAPS/TLS connections
  • v0.5.1: Update the Egg configuration file and the author contact details

Author/Contributors

Author: eblot
Contributors: wichert#wiggy.net, nguyen.antoine#wanadoo.fr

TagIt(eblot,0.10,plugin)?