LemonLDAP::NG

Lemonldap::NG is a modular Web-SSO based on Apache::Session modules. It simplifies the build of a protected area with a few changes in the application. It manages both authentication and authorization and provides headers for accounting. So you can have a full AAA protection for your web space as described below.

Lemonldap::NG is a complete rewrite of Lemonldap. All components needed to use it and to aminister it are included in the tarball. Contrary, all modules developed for Lemonldap may not work with Lemonldap::NG.

Architecture

Lemonldap::NG est composed by 3 elements and 3 databases :

lemonldap-ng-architecture.png

Lemonldap::NG components :

  • the Manager used to manage Lemonldap::NG configuration,
  • the Portal used to authenticate users,
  • Apache modules used to protect applications. They can protect an Apache area which can be a reverse-proxy. In this case, it is recommended to securise the link between the reverse-proxy and the hidden server because access can be done without authentication to this server. A simple .htaccess or an SSL handshake can be used depending on the security level of the host network.
Three databases are required :
  • the configuration database : by default, it's a simple directory, but you can use a network database to share configuration if all the Lemonldap::NG components aren't on the same physical server,
  • the LDAP server : in addition to the authentications (that can be done by another mechanism as X509 certificates), it is used to load user attributes and calculate the rights,
  • the sessions database : Lemonldap::NG uses Apache::Session modules to manage sessions. By default, it uses Apache::Session::File module and so, this database is a simple directory. Using Apache::Session::MySQL for example, the database can be used on a network so Lemonldap::NG can works on several physical servers.

Kinematics

lemonldap-ng-cinematique.png

Detail of operations :

  • 1 and 2 : non-authenticated users (ie without valid cookie) are redirected to the portal,
  • 3 : authentication request (login password validated on LDAP server or other mechanism),
  • 4 : recovery ok user attributes,
  • 5 : calculation of the additional attributes asked in the configuration (macros and groups) and storage of the user datas in the sessions database,
  • 6 : cookie generation and redirection to the asked URL,
  • 7 : interception of the cookie by the agent of protection (Apache module) and recovery of the user datas,
  • 8 : checking of the access authorization to the asked URL and transmission to the application (real application or reverse-proxy) if granted,
  • 9 and 10 : other request are treated directly with the use datas stored in the local cache. Access grant is calculated at each request.
When the authenticated user tries to access to another protected server, only phases 7 to 10 are replayed in all transparency for the user.

Authentication, Authorization and Accounting mechanisms

All parameters described here can be edited by the administration interface (See Manager demonstration).

Authentication

If a user isn't authenticated and attemps to connect to an area protected by a Lemonldap::NG compatible handler, he is redirected to a portal. The portal authenticates user with a ldap bind by default, but you can also use another authentication sheme like using x509 user certificates (see Lemonldap::NG::Portal::AuthSSL(3) for more).

Lemonldap use session cookies generated by Apache::Session so as secure as a 128-bit random cookie. You may use the securedCookie options to avoid session hijacking.

You have to manage life of sessions by yourself since Lemonldap::NG knows nothing about the L module you've choosed, but it's very easy using a simple cron script because Lemonldap::NG::Portal stores the start time in the _utime field.

By default, a session stay 10 minutes in the local storage, so in the worst case, a user is authorized 10 minutes after he lost his rights.

Authorization

Authorization is controled only by handlers because the portal knows nothing about the way the user will choose. When configuring your Web-SSO, you have to:

  • choose the ldap attributes you want to use to manage accounting and authorization.
  • create Perl expressions to define user groups (using ldap attributes)
  • create an array foreach virtual host associating URI regular expressions and Perl expressions to use to grant access.
Example (See Lemonldap::NG::Manager::Conf(3) to see how configuration is stored) :
  • Exported variables :
# Custom-Name    => LDAP attribute
cn               => cn
departmentUID    => departmentUID
login            => uid
  • User groups :
# Custom-Name => group definition
group1        => { $departmentUID eq "unit1" or $login = "user1" }
  • Area protection: each VirtualHost has its own configuration associating URL regexp to Perl expression
    • www1.domain.com :
^/protected/.*$  => $groups =~ /\bgroup1\b/
default          => accept
    • www2.domain.com :
^/site/.*$       => $uid eq "admin" or $groups =~ /\bgroup2\b/
^/(js|css)       => accept
default          => deny

Note: \b means start or end of a word in PCRE (Perl Compatible Regular Expressions)

Performance

You can use Perl expressions as complicated as you want and you can use all the exported LDAP attributes (and create your own attributes: with 'macros' mechanism) in groups evaluations, area protections or custom HTTP headers (you just have to call them with a "$").

ou have to be careful when choosing your expressions:

  • groups and macros are evaluated each time a user is redirected to the portal,
  • virtual host rules and exported headers are evaluated for each request on a protected area.
It is also recommanded to use the groups mechanism to avoid having to evaluate a long expression at each HTTP request :
^/protected/.*$   => $groups =~ /\bgroup1\b/

You can also use LDAP filters, or Perl expression or mixed expressions in groups definitions. Perl expressions has to be enclosed with {} :

group1 => (|(uid=xavier.guimard)(ou=unit1))
group1 => {$uid eq "xavier.guimard" or $ou eq "unit1"}
group1 => (|(uid=xavier.guimard){$ou eq "unit1"})

It is also recommanded to use Perl expressions to avoid requiering the LDAP server more than 2 times per authentication.

Accounting

Logging portal access

Lemonldap::NG::Portal doesn't log anything by default, but it's easy to overload log method for normal portal access.

Logging application access

Because a Web-SSO knows nothing about the protected application, it can't do more than logging URL. As Apache does this fine, Lemonldap::NG::Handler(3) gives it the name to used in logs. The whatToTrace parameter indicates which variable Apache has to use ($uid by default).

The real accounting has to be done by the application itself which knows the result of SQL transaction for example.

Lemonldap::NG can export HTTP headers either using a proxy or protecting directly the application. By default, the Auth-User field is used but you can change it using the exportedHeaders parameters (in the Manager, each virtual host as custom headers branch). This parameters contains an associative array per virtual host :

  • keys are the names of the choosen headers,
  • values are Perl expressions where you can use user datas stored in the global storage.
Example:
  • www1.domain.com :
Auth-User     => $uid
Unit          => $ou
  • www2.domain.com :
Authorization => "Basic ".encode_base64($employeeNumber.":dummy")
Remote-IP     => $ip

Installation

Warnings :

  • Lemonldap::NG is a different project than Lemonldap and contains all you need to use and administer it. So softwares, like Lemonldap webmin module, may not work with Lemonldap::NG.
  • The Apache module part (Lemonldap::NG::Handler) works both with Apache 1.3.x and 2.x ie mod_perl 1 and 2 (but not with mod_perl 1.99). Portal and Manager act as CGI, so they can work everywhere.
  • Lemonldap::NG configuration has to be edited using the manager unless you know exactly what you are doing. The parameters discussed below are all in the configuration tree.
See the full documentation page for a complete installation procedure.

Session storage system

Lemonldap::NG use 3 levels of cache for authenticated users :

  • an Apache::Session::* module used by lemonldap::NG::Portal to store authenticated user parameters,
  • a Cache::Cache* module used by Lemonldap::NG::Handler to share authenticated users between Apache's threads or processus and of course between virtual hosts on the same machine,
  • Lemonldap::NG::Handler variables : if the same user use the same thread or processus a second time, no request are needed to grant or refuse access. This is very efficient with HTTP/1.1 Keep-Alive system.
So the number of request to the central storage is limited to 1 per active user each 10 minutes.

Lemonldap::NG is very fast, but you can increase performance using a Cache::Cache module that does not use disk access.

Author

Xavier Guimard, <x.guimard@free.fr>

Copyright and licence

Copyright © 2005-2007 by Xavier Guimard <x.guimard@free.fr>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.