Multiple backends stack

Authentication Users Password

Presentation

This backend allows one to chain authentication method, for example to failback to LDAP authentication if Remote authentication failed…

Configuration

You have to use Multiple as authentication modul (this will also force Multiple for the users module). Then go in Multiple parameters to define the modules to chain for authentication and users. Modules are separated by semi-colons/

For example:

CAS;LDAP

If CAS failed, LDAP will be used.

You can also add a condition. Example:

Remote $ENV{REMOTE_ADDR}=~/^192/;LDAP $ENV{REMOTE_ADDR}!~/^192/'
Multiple will try to use the same module for authentication and users. Example, if you have DBI;LDAP and DBI failed for authentication, it will try first to call LDAP as user database.

Advanced configuration

The Multiple system can :

  • stack several times the same module with a different name
  • overload any LL::NG parameter when a specific backend is used
Overloading is not available trough the Manager

To stack several times the same module, use “#name” with different names. Example:

LDAP#Openldap; LDAP#ActiveDirectory

Then you can have different parameters for each stored in a Perl hash entry named multi:

multi => {
    'LDAP#Openldap' => {
      'ldapServer' => 'ldap1.example.com',
      'LDAPFilter' => '(uid=$user)',
    },
    'LDAP#ActiveDirectory' => {
      'ldapServer' => 'ldaps://ad.example.com',
      'LDAPFilter' => '(&(sAMAccountName=$user)(objectClass=person))',
    }
},

This key must be stored directly in lemonldap-ng.ini:

[portal]
multi = {'LDAP#Openldap'=>\
  {'ldapServer'=>'ldap1.example.com',\
  'LDAPFilter'=>'(uid=$user)'},\
'LDAP#ActiveDirectory'=>\
  {'ldapServer'=>'ldaps://ad.example.com',\
  'LDAPFilter'=>'(&(sAMAccountName=$user)(objectClass=person))'}\
}

Known problems

AuthApache authentication

When using this module, LL::NG portal will be called only if Apache does not return “401 Authentication required”, but this is not the Apache behaviour: if the auth module fails, Apache returns 401.

To bypass this, follow the documentation of AuthApache module

SSL authentication

To chain SSL, you have to set “SSLRequire optional” in Apache configuration, else users will be authenticated by SSL only.

Complex use case

Here is a complex use case involving :

  • multiple authentication with
    1. SSL
    2. Kerberos
    3. LDAP
  • LemonLDAP::NG as a SAML IdP

The URLs will be:

In this case, redirection script described in the kerberos configuration page is insufficient. You have to transfer every parameter in SAML request, so rather use this redirection script instead:

#!/usr/bin/perl
use CGI ':cgi-lib';
use strict;
use MIME::Base64;
use CGI::Carp 'fatalsToBrowser';
 
my $uri = $ENV{"REDIRECT_URL"};
$uri .= "?".$ENV{"REDIRECT_QUERY_STRING"};
$uri =~ s/\/kerberos//;
print CGI::header(-Refresh => '0; URL=https://auth.example.com'.$uri);
exit(0);

You also have to make LemonLDAP::NG tolerant to the Path in order to have SAML request correctly detected. To do this, go in the manager, and configure the SAML Path (General Parameters > Issuer modules > SAML > Path) with a regular expression:

^/(kerberos/saml/|saml/)

Don't forget to configure your authentication modules accordingly. Especially the chained authentications: General Parameters > Authentication parameters > Multi parameters > Authentication stack string

SSL;Apache;LDAP

Finally, don't forget to configure the portal virtual host with all the authentication parameters needed. Take a special care to the added RewriteRule in the SAML issuer section:

<VirtualHost "*:443">
    ServerName auth.example.com

    SSLEngine on

    SSLCertificateFile      /etc/httpd/ssl/auth.example.com.crt
    SSLCertificateKeyFile   /etc/httpd/ssl/auth.example.com.key
    SSLCertificateChainFile /etc/httpd/ssl/chain.pem

    SSLVerifyClient optional
    SSLCACertificateFile    /etc/httpd/ssl/ca.crt
    SSLVerifyDepth 10
    SSLOptions +StdEnvVars

    LogLevel warn
    ErrorLog /var/log/httpd/error_log

    # DocumentRoot
    DocumentRoot /var/lib/lemonldap-ng/portal/
    <Directory /var/lib/lemonldap-ng/portal/>
        Require all granted
        Options +ExecCGI +FollowSymLinks
    </Directory>

    Alias /kerberos /var/lib/lemonldap-ng/portal/
    <Location /kerberos>
      Options +execCGI
      ErrorDocument 401 /redirectKRB.pl

      AuthType Kerberos
      KrbMethodNegotiate On
      KrbMethodK5Passwd Off
      AuthName "REALM.COM"
      KrbAuthRealms REALM.COM
      Krb5KeyTab /etc/httpd/keytabs/auth.keytab
      KrbVerifyKDC Off
      KrbServiceName Any
      Require valid-user
    </Location>

[...]

    # SAML2 Issuer
    <IfModule mod_rewrite.c>
        RewriteEngine On
        RewriteRule ^/saml/metadata /metadata.pl
        RewriteRule ^/saml/.* /index.pl
        RewriteRule ^/kerberos/saml/.* /index.pl
    </IfModule>

[...]
</VirtualHost>