Configuring authentication with openLDAP server

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Configuring authentication with openLDAP server

LDAP server configuration

Necessary schema

Schema file nis.schema should be included in slapd.conf for being able to add posixAccount or shadowAccount entry.

User accounts

First user accounts or groups should be created on ldap server. A sample ldif file that can be used create a user is:

dn: uid=saurabh,ou=people,dc=sbarjatiya,dc=com
objectClass: top
objectClass: account
objectClass: posixAccount
objectClass: shadowAccount
cn: Saurabh Barjatiya
uid: saurabh
uidNumber: 3000
gidNumber: 3000
homeDirectory: /home/saurabh
loginShell: /bin/bash
gecos: OFQ F2, IIIT Hyderabad
userPassword: iiit123
shadowLastChange: 0
shadowMax: 99999
shadowWarning: 99999

Group accounts

To create a group account sample ldif file is:

dn: cn=group1,ou=groups,dc=sbarjatiya,dc=com
objectClass: top
objectClass: posixGroup
cn: group1
userPassword: iiit123
gidNumber: 3000
memberuid: saurabh

To add member to group sample ldif file is:

dn: cn=group1,ou=groups,dc=sbarjatiya,dc=com
changetype: modify
add: memberuid
memberuid: saurabh.barjatiya

To delete member from group sample ldif file is:

dn: cn=group1,ou=groups,dc=sbarjatiya,dc=com
changetype: modify
delete: memberuid
memberuid: saurabh.barjatiya

Linux host authentication

To configure a linux host to authenticate from ldap server use following steps:

1. yum install openldap-clients openldap nss-pam-ldapd
2. Check if sssd package is installed using 'rpm -qa | grep sssd'. If it is installed remove it using 'yum remove sssd'. If some ipa-* packages also need to be removed then it is fine.
3. Start setup program and use following steps:
   1. Choose 'Authentication configuration'
   2. Select 'Use ldap'
   3. Select 'Use ldap authentication'
   4. Go to next screen with next button
   5. Do not check Use TLS
   6. Enter server name, for example ldap://ldap.virtual-labs.ac.in/
   7. Enter server basedn, for example, dc=virtual-labs,dc=ac,dc=in
   8. Complete configuration with ok button
   9. Close setup program with quit button
4. Edit '/etc/hosts' file and add static entry for ldap server, for example '12.4.12.152 ldap.virtual-labs.ac.in'
5. Edit '/etc/pam_ldap.conf' and replace lines at end that start with uri with following:

   uri ldaps://ldap.virtual-labs.ac.in/
   ssl on
   tls_cacertfile /etc/openldap/certs/ca.crt
   pam_password md5

6. Go to '/etc/openldap/certs' and put CA certificate in the directory with name ca.crt
7. Edit '/etc/nslcd.conf' and replace lines at end that start with uri with following:

   uri ldaps://ldap.virtual-labs.ac.in/
   base dc=virtual-labs,dc=ac,dc=in
   ssl on
   timelimit 10
   idle_timelimit 30
   reconnect_sleeptime 30
   reconnect_retrytime 90
   tls_reqcert hard
   tls_cacertfile /etc/openldap/certs/ca.crt

8. Edit '/etc/pam.d/sshd' and add following line after last 'session required' line

   session    required     pam_mkhomedir.so skel=/etc/skel/ umask=0077

9. Edit '/etc/nsswitch.conf' and for 'hosts' choose value 'files ldap dns'

   Note that you should not see sss anywhere in this file. If you see sss instead of ldap then you have forgotten to remove sssd as mentioned earlier in these steps

10. Use 'service nscld restart'
11. Do 'chkconfig nslcd on'

Verifying setup

To verify whether authentication setup is working or not try commands:

getent hosts
getent passwd
getent group
getent shadow

One can also read '/var/log/messages' and '/var/log/secure' while trying to login from a ldap user, if configuration does not seem to succeed.

Restricting logins to specific users and posixGroups

To restrict logins on a machine to specific users or posixGroups use:

1. Edit file '/etc/pam.d/sshd' and add following line

   auth     required     pam_access.so

2. Edit file '/etc/security/access.conf' and add line similar to:

   - : ALL EXCEPT root (admin) : ALL

An access.conf configuration line has three parameters separated by :

1. First '+' or '-' to indicate whether to allow or deny
2. Second list of users and groups. Group names can be enclosed in round brackets () to be more explicit that given name is of group. We can also use word ALL to indicate ALL. We can also use word EXCEPT to create exceptions from ALL for specific users and groups.
3. Third is the location from where when user logins should this rule apply.

Read the comments in file '/etc/security/access.conf' to understand use of access.conf in better way.

Password change

If user tries to ssh or login using credentials then he/she would be forced to change password on first login. During password change user would be asked for existing ldap password again through which user has logged in. Then user would have option of entering new password twice. After password is set user would be logged off automatically. Then user can login again by using ssh and entering new password.

Mediawiki Authentication

Mediawiki supports LDAP based authentication with extension 'LdapAuthentication'. To configure mediawiki authentication using ldap use: Note that LDAP authentication may not work with SQLite database back-end

1. yum -y install php-ldap
2. service httpd restart
3. Download latest LdapAuthentication plugin for installed media-wiki version from http://www.mediawiki.org/wiki/Special:ExtensionDistributor/LdapAuthentication
4. Extract the downloaded file in extensions folder
5. Add following lines to 'LocalSettings.php' file for a non-SSL, non-TLS LDAP server with anonymous read enabled:

   require_once("$IP/extensions/LdapAuthentication/LdapAuthentication.php");
   $wgAuth = new LdapAuthenticationPlugin();
   
   $wgLDAPDomainNames = array('Domain_name',);
   $wgLDAPServerNames = array('Domain_name' => 'LDAP_server_IP_or_FQDN',);
   
   #Avoid using local groups.  This is recommended by plugin author
   #$wgLDAPUseLocal = false;
   
   #This can be uncommented on test machines to debug ldap issue, not meant for production.
   #$wgLDAPDebug = 3;
   #$wgDebugLogGroups['ldap'] = '/tmp/debug.log';
   
   $wgLDAPEncryptionType = array('Domain_name' => 'clear',);
   $wgLDAPSearchAttributes = array('Domain' => 'uid',);
   $wgLDAPBaseDNs = array('Domain_name' => 'Base_dn',);
   $wgLDAPPreferences = array('Domain_name' => array('email' => 'mail', 'realname' => 'displayName', 'nickname' => 'cn',),);
   $wgLDAPLowerCaseUsername = array('Domain_name' => true, );
   $wgLDAPGroupUseFullDN = array('Domain_name' => false, );
   $wgLDAPGroupObjectclass = array('Domain_name' => 'posixGroup',);
   $wgLDAPGroupAttribute = array('Domain_name' => 'memberUid',);
   $wgLDAPGroupNameAttribute = array('Domain_name' => 'cn',);
   
   #This should be avoided on really large setup as per plugin author documentation
   $wgLDAPGroupsPrevail = array('Domain_name' => true,);

   Here Domain_name should be replaced with recognizable name which would also be shown to user on login page. Base_dn should be replaced by LDAP base_dn. Few settings such as User and Group search dn have been omitted for simplicity. Note that all arrays values can take multiple key, value pairs but only one is used in this example for simplicity. In large setups one can put multiple values in necessary arrays.

6. To force user to be from a specific LDAP group also append:

   $wgLDAPRequiredGroups = array('Domain_name' => array('Required_Group',),);

   Here Required_Group is dn for group for which user must be a member

7. To ensure users belonging to a particular group can never login use:

   $wgLDAPExcludedGroups = array('Domain_name' => array('Exclude_Group',),);

   Here Exclude_Group is dn for group whose members would be denied access.

ldap_domains table does not exists error

It is possible that ldap_domains table does not exists error is shown. To solve that login into MySQL database used by mediawiki and use:

     CREATE TABLE ldap_domains(domain_id int not null primary key auto_increment, domain varchar(255) binary not null, user_id int not null);
     CREATE INDEX user_id on ldap_domains(user_id);

The queries have been obtained using schema/ldap-mysql.sql file from LdapAuthentication plugin source files.

Refer http://www.mediawiki.org/wiki/Extension:LDAP_Authentication/Configuration_Options for more details

Squid proxy authentication

To enable ldap based authentication for squid use:

1. First find location of program named 'squid_ldap_auth' and run it as follows:

   /usr/lib64/squid/squid_ldap_auth -b "<base-dn>" -f "uid=%s" <ldap-server>

   The command will not give any prompt and expect '<username> <password>' as input.

2. If the after supply username and password the response is ok, then ldap authentication from proxy server is working properly, else debug ldap issues
3. Edit squid.conf and add following lines:

   acl login-users src <IP-range>
   
   auth_param basic program /usr/lib64/squid/squid_ldap_auth -b "<base-dn>" -f "uid=%s" -h <ldap-server>
   acl ldapauth proxy_auth REQUIRED
   http_access allow login-users ldapauth

   This would cause all users connecting from given IP-range to be authenticated. For others one can use 'http_access allow all' or 'http_access deny all' etc. based on situation.

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