wiki:LdapPlugin

Version 10 (modified by eblot, 9 years ago) (diff)

Change tag version

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 to store permissions (both users and groups permissions) in the LDAP directory itself rather than in the SQL backend.

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

This software is licenced with the same license as Trac.

Requirements

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, as well as on a Windows XP SP2 workstation, both running Python 2.3 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-py2.3.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.

Here is an example of a typical LDAP section of an Apache2 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>

Configuration

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

  1. Create a new section [ldap] and,
  2. Add the magic keyword module so that the Trac engine loads and uses this extension.
  3. Optionnally add the path to your plugin directory
  4. Configure the LDAP directives to fit your LDAP server configuration

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

[ldap]
# enable LDAP support for Trac
enable = false
# LDAP directory host
host = localhost
# LDAP directory port
port = 389
# BaseDN
basedn = dc=example,dc=com
# BaseDN for users (defaults to basedn)
user_basedn = dc=example,dc=com
# BaseDN for group of names (defaults to basedn)
group_basedn = dc=example,dc=com
# 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
# user for authenticated group bind
group_user = 
# password for authenticated group bind
group_passwd =
# whether to perform an authenticated bind for permision store operations
store_bind = false
# user for authenticated store bind
store_user =
# password for authenticated store bind
store_passwd =
# global permissions (vs. per-environment permissions)
global_perms = false

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
store_bind = true
store_user = cn=tracadmin,dc=example,dc=org
store_passwd = mypasswd

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
group_user = joeuser
group_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]
group_bind = true
group_user = joeuser
group_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. To achieve this setting, add the following line to the main [trac] section of your trac.ini configuration file:

[trac]
# ...
permission_store = LdapPermissionStore

The extension differenciates 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 differenciate 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.

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.

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.
  • 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
  • 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.

Author/Contributors

Author: eblot
Contributors:

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