LemonLDAP::NG is a modular WebSSO (Single Sign On) 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.
- Manager: used to manage LemonLDAP::NG configuration and to explore sessions. Dedicated to administrators
- Handler: Apache modules used to protect applications
We split databases in two categories:
- External databases: not managed by LemonLDAP::NG, for example user database
- Internal databases: only used by LemonLDAP::NG
Main external databases are:
- Authentication: how authenticate users
- User: where collect user data
- Password: where change the password
Main internal databases are:
- User tries to access protected application, his request is catched by Handler
- SSO cookies is not detected, so Handler redirects user to Portal
- User authenticates on Portal
- Portal checks authentication
- If authentication succeed, Portal collect user data
- Portal creates a session to store user data
- Portal gets the session key
- Portal creates SSO cookies with session key as value
- User is redirected on protected application, with his new cookie
- Handler gets session get from cookie and gets session
- Handler stores user data in its cache
- Handler check access rule and send headers to protected applications
- Protected application sends response to Handler
- Handler sends the response to user
Handler will then check SSO cookies for each HTTP request.
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.
The session expires after 20 hours by default.
- Handlers have a session cache, with a default lifetime of 10 minutes. So for Handler on different physical servers than the Portal, a user with an expired session can still be authorized still the cache expires.
- Sessions are deleted by a scheduled task. Don't forget to install cron files !
Cross Domain Authentication (CDA)
- 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
If a user is not authenticated and attempts to connect to an area protected by a LemonLDAP::NG compatible Handler, he is redirected to a 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
- 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 is controlled only by Handlers. An authorization is defined by:
- An URL pattern (or
defaultto match other URLs)
- An access rule
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_app_sso: catch logout request
- Perl expression: perl code snippet that returns 0 or 1
- Accept all authenticated users:
- URL pattern:
- Access rule:
- Restrict /admin to administrators group
- URL pattern:
- Access rule:
$groups =~ /\badministrators\b/
\bmeans start or end of a word in PCRE (Perl Compatible Regular Expressions)
See Writing rules and headers chapter.
Logging portal access
Portal produce a
notice message in Apache logs or syslog when a user authenticates (or fails to authenticate) and logs out.
Logging application access
Handler inform Apache of connected user (parameter
whatToTrace), so you can see user login in Apache 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:
- A name
- A value
The header value is a Perl expression, returning a string.
- Send login in Auth-User:
- Send “Lastname, firstname” in Auth-Name:
$sn + “, ” + $gn
See Writing rules and headers for more.