These instructions have nothing special about them. There are many such instructions on the internet.
The purpose here is only as reference for myself and maybe you as well.

Here I’m assuming that you have installed openLDAP and created users and groups in LDAP server.
In the following examples the users and groups login names are set in the ‘cn‘ field of each user.
I used phpLDAPAdmin web interface to enter the Users and groups.
In this interface I used the following templates:
Users: Default
Groups: Generic: Posix Group

Here is an example of users web authentication:
Requires Apache modules: mod_ldap and mod_authnz_ldap
cd /etc/apache2/mods-enabled
ln -s ../mods-available/ldap.load
ln -s ../mods-available/authnz_ldap.load

Note: We want users ‘john’ and ‘peter’ to be allowed in an area called /docs/private.
Apache configuration:

Single Users Web authentication


In this case although ‘john’ and ‘peter’ are belonging to the group ‘admins’ we authenticate only the single users without any reference to their group.
Syntax of AuthLDAPURL
Syntax: Protocol://ServerName/SearRealmFilter?searchAttribute
Description:
Protocol: ldap
ServerName: 127.0.0.1
SearRealmFilter: ou=People,dc=itmatrix,dc=srv
SearchAttribute: cn
Apache Directives
<Location /docs/private>
    AuthType Basic
    AuthBasicProvider ldap
    AuthName "LDAP Auth"
    AuthzLDAPAuthoritative On
    AuthLDAPURL "ldap://127.0.0.1/ou=People,dc=itmatrix,dc=srv?cn"
    Require ldap-user john peter
</Location>

Group Web authentication


In order to authenticate different locations of an SVN tree we need to create different configuration files
for each location. Here is an example of the group authentication of one area.

IMPORTANT: The primary group of each user MUST also have the user in its ‘secondary group list’
eg.
User:            michel
Primary group:   admin
Secondary group: admin
Secondary group: sales
Secondary group: pr
Apache Directives
<Location /docs/private>
    Order deny,allow
    Deny from All
    #
    AuthType Basic
    AuthBasicProvider ldap
    AuthName "LDAP Auth"
    AuthLDAPURL "ldap://127.0.0.1/ou=People,dc=itmatrix,dc=srv?cn"
    AuthzLDAPAuthoritative On
    Satisfy any
    #
    # =========== GROUP auth =========================
    # Group auth - Using Posix Group Template and Default User Template in phpLDAPAdmin
    # Standard Group Attribute where the secondary users IDs are stored
    AuthLDAPGroupAttribute memberUid
    #
    # Group record doesn't store the full DN, therefore turning it off
    AuthLDAPGroupAttributeIsDN off
    #
    # Allow users of secondary and of primary group 'sales' which have the GID=1004
    Require ldap-group cn=sales,ou=Group,dc=itmatrix,dc=srv
    Require ldap-attribute gidNumber=1004
    #
    #----------- OPTIONAL GROUP auth---------------
    # Allow users of secondary and of primary group 'pr' which have the GID=1002
    Require ldap-group cn=pr,ou=Group,dc=itmatrix,dc=srv
    Require ldap-attribute gidNumber=1002
</Location>
More information at: http://www.linux.com/archive/feature/120050