Presentation
LemonLDAP::NG is a modular WebSSO (Single Sign On) written in Perl.
It is highly customizable, and can be deployed in many different environments
and for many different uses. It manages both authentication and authorization
and provides customizable logging for accounting. So you can have a full AAA
protection for your applications.
Architecture

Main components
- Manager: used to manage LemonLDAP::NG configuration and to
explore sessions. Dedicated to administrators
- Portal: used to authenticate
users, display applications list and provides identity provider
service (SAML,
OpenID,
CAS).
Futhermore, Portal offers many other features (see
portal for more)
- Handler: used to protect applications which can read HTTP headers
or environment variables to get user information
Databases
Attention
We use “database” as a generic term for backends that are not included with
LemonLDAP::NG but that we need in order to provide the SSO service.
They can be a LDAP directory, a SQL database server, or even a simple local
file.
We split databases in two categories:
- External databases: are not managed by LemonLDAP::NG. Data is externally
provided and LemonLDAP::NG generally just needs to read it.
- Internal databases: its data is controlled by LemonLDAP::NG
Main
external databases
are:
- Authentication: how users are authentified (password, certificate, etc.)
- User: where to find user attributes
- Password: how user passwords are changed
- Registration: where new users are created
- Second factors: how second factors are validated
Main internal databases are:
- Configuration:
where configuration is stored. This does not include web server
configuration which is not managed by LemonLDAP::NG
- Sessions:
where sessions are stored.
- Notifications:
messages displayed to connected users
- Cache: cache for configuration and sessions
Kinematics
Handler protection

- User tries to access a protected application, his request is caught by Handler
- SSO cookie is not detected, so Handler redirects user to Portal
- User authenticates on Portal
- Portal checks authentication
- If authentication succeeds, Portal collects user data
- Portal creates a session to store user data
- Portal gets the session Id
- Portal creates SSO cookie with the session Id as value
- User is redirected on protected application, with a SSO cookie
- Handler reads session Id from the cookie and retrieves user session data
- Handler stores user data in its cache
- Handler checks access rules and sends headers to the protected application
- Protected application sends response to Handler
- Handler forwards the response to the user
Then handler will check SSO cookies for each HTTP request.
Logout
Default use case:
- User clicks on the logout link in Portal
- Portal destroys session and redirects user on itself with an empty
SSO cookies
- User is redirected on portal and his SSO cookies is empty
LemonLDAP::NG is also able to
catch logout request
on protected applications, with different behavior:
- SSO logout: the request is not forwarded to application, only the
SSO session is closed
- Application logout: the request is forwarded to application but
SSO session is not closed
- SSO and Application logout: the request is forwarded to
application and SSO session is closed
After logout process, the user is redirected on portal, or on a configured URL.
Session expiration
The session expires after 20 hours by default.
This duration can be set in the manager’s Configuration tab (General Parameters > Sessions > Sessions Timeout).
Attention
- Handlers have a session cache, with a default lifetime of 10 minutes.
So for Handlers embedded by different physical servers than the Portal, a user
with an expired session can still be authorized until the cache expiration.
- Sessions are deleted by a scheduled task. Do not forget to install cron files!
Cross Domain Authentication (CDA)
Note
For security reason, a cookie provided for a domain cannot be sent
to another domain. To extend SSO on several domains, a cross-domain
mechanism is implemented in LemonLDAP::NG.
- User owns
SSO cookies on the
main domain (see Login kinematics)
- User tries to access a protected application in a different domain
- Handler does not see
SSO cookies
(because it is not in main domain) and redirects user on Portal
- Portal recognizes the user with its
SSO cookies, and
see he is coming from a different domain
- Portal redirects user on protected application with a token as URL
parameter. The token is linked to a session which contains the real
session ID
- Handler detects URL parameter, gets the real session ID, delete the
token session and creates a
SSO cookies on its
domain, with session ID as value
Authentication, Authorization and Accounting (AAA) mechanisms
Authentication
If a user is not authenticated and attempts to connect to an area
protected by a LemonLDAP::NG compatible Handler, he is redirected to the
portal.
Authentication process main steps are:
- Control asked URL: prevent XSS attacks and bad redirections
- Control existing session: detect SSO session, apply configured
constraints (1 session per user, 1 session per IP, ...)
- Extract form info: get login/password, certificate, environment
variable (depending on authentication module)
- Get user info: contact user database to collect attributes
- Ask for second factor if required: TOTP, U2F key, etc...
- Set macros: compute configured macros
- Set groups: request user database to find groups
- Set local groups: compute configured groups
- Authenticate: contact authentication database to check
credentials
- Grant session: check rights to open SSO session
- Store: store user info in session database
- Build cookie: build
SSO cookies with
session ID
- Redirect: redirect user on protected application or on Portal
(applications menu)
LemonLDAP::NG
SSO cookies are
generated by
Apache::Session,
they are as secure as a 128-bit random cookie. You may use the
securedCookie options
to avoid session hijacking. (since version 1.4.0 you can use SHA256 for
generating safer cookies)
Authorization
Authorization is controlled only by Handlers. An authorization is
defined by:
- An URL pattern (or default to match other URLs)
- An access rule
Note
Authorizations are defined inside a virtualhost and takes effect
only on it. There are no global authorizations except the right to
open a session in the portal.
Access rules values can be:
- accept: all authenticated users can pass
- deny: nobody is welcomed
- skip: all is open!
- unprotect: all is open, but authenticated users are seen as
authenticated
- logout_sso, logout_app, logout_app_sso: catch logout
request
- Perl expression: perl code snippet that returns 0 or 1
Some examples:
- Accept all authenticated users:
- URL pattern: default
- Access rule: accept
- Restrict /admin to administrators group
- URL pattern: ^/admin/
- Access rule: $groups =~ /\badministrators\b/
Tip
\b means start or end of a word in PCRE (Perl Compatible
Regular Expressions)
See
Writing rules and headers
chapter.
Accounting
Logging portal access
Portal produce a notice message in
Web server logs or syslog when a user
authenticates (or fails to authenticate) and logs out.
Logging application access
Handler informs Web server of connected user (parameter
whatToTrace), so you can see user login in Web server access logs.
The real accounting has to be done by the application itself since SSO
logs can not understand transactions.
LemonLDAP::NG can export
HTTP headers
either using a proxy or protecting directly the application.
An HTTP header is defined by:
Note
Headers are defined inside a virtualhost and take effect only on
it. There are no global headers.
The header value is a Perl expression, returning a string.
Some examples:
- Send login in Auth-User:
- Name: Auth-User
- Value: $uid
- Send “Lastname, firstname” in Auth-Name:
- Name: Auth-Name
- Value: $sn + ", " + $gn
See
Writing rules and headers
for more.