LDAP Authentication

The <ldap-server> element can also be used to create an embedded server, which can be very useful for testing and demonstrations. In this case you use it without the url attribute:

  <ldap-server root="dc=springframework,dc=org"/>
 
    

Here we've specified that the root DIT of the directory should be “dc=springframework,dc=org”, which is the default. Used this way, the namespace parser will create an embedded Apache Directory server and scan the classpath for any LDIF files, which it will attempt to load into the server. You can customize this behaviour using the ldif attribute, which defines an LDIF resource to be loaded:

  <ldap-server ldif="classpath:users.ldif" />
        

This makes it a lot easier to get up and running with LDAP, since it can be inconvenient to work all the time with an external server. It also insulates the user from the complex bean configuration needed to wire up an Apache Directory server. Using plain Spring Beans the configuration would be much more cluttered. You must have the necessary Apache Directory dependency jars available for your application to use. These can be obtained from the LDAP sample application.

This is the most common LDAP authentication scenario.

  <ldap-authentication-provider user-dn-pattern="uid={0},ou=people"/>
                     

This simple example would obtain the DN for the user by substituting the user login name in the supplied pattern and attempting to bind as that user with the login password. This is OK if all your users are stored under a single node in the directory. If instead you wished to configure an LDAP search filter to locate the user, you could use the following:

  <ldap-authentication-provider user-search-filter="(uid={0})"
          user-search-base="ou=people"/>
                    

If used with the server definition above, this would perform a search under the DN ou=people,dc=springframework,dc=org using the value of the user-search-filter attribute as a filter. Again the user login name is substituted for the parameter in the filter name. If user-search-base isn't supplied, the search will be performed from the root.

How authorities are loaded from groups in the LDAP directory is controlled by the following attributes.

So if we used the following configuration

  <ldap-authentication-provider user-dn-pattern="uid={0},ou=people"
          group-search-base="ou=groups" />
    

and authenticated successfully as user “ben”, the subsequent loading of authorities would perform a search under the directory entry ou=groups,dc=springframework,dc=org, looking for entries which contain the attribute uniqueMember with value uid=ben,ou=people,dc=springframework,dc=org. By default the authority names will have the prefix ROLE_ prepended. You can change this using the role-prefix attribute. If you don't want any prefix, use role-prefix="none". For more information on loading authorities, see the Javadoc for the DefaultLdapAuthoritiesPopulator class.

The authenticator is also responsible for retrieving any required user attributes. This is because the permissions on the attributes may depend on the type of authentication being used. For example, if binding as the user, it may be necessary to read them with the user's own permissions.

There are currently two authentication strategies supplied with Spring Security:

The beans discussed above have to be able to connect to the server. They both have to be supplied with a SpringSecurityContextSource which is an extension of Spring LDAP's ContextSource. Unless you have special requirements, you will usually configure a DefaultSpringSecurityContextSource bean, which can be configured with the URL of your LDAP server and optionally with the username and password of a "manager" user which will be used by default when binding to the server (instead of binding anonymously). For more information read the Javadoc for this class and for Spring LDAP's AbstractContextSource.

Often a more complicated strategy than simple DN-matching is required to locate a user entry in the directory. This can be encapsulated in an LdapUserSearch instance which can be supplied to the authenticator implementations, for example, to allow them to locate a user. The supplied implementation is FilterBasedLdapUserSearch.

After authenticating the user successfully, the LdapAuthenticationProvider will attempt to load a set of authorities for the user by calling the configured LdapAuthoritiesPopulator bean. The DefaultLdapAuthoritiesPopulator is an implementation which will load the authorities by searching the directory for groups of which the user is a member (typically these will be groupOfNames or groupOfUniqueNames entries in the directory). Consult the Javadoc for this class for more details on how it works.

If you want to use LDAP only for authentication, but load the authorities from a difference source (such as a database) then you can provide your own implementation of this interface and inject that instead.

A typical configuration, using some of the beans we've discussed here, might look like this:

<bean id="contextSource"
        class="org.springframework.security.ldap.DefaultSpringSecurityContextSource">
  <constructor-arg value="ldap://monkeymachine:389/dc=springframework,dc=org"/>
  <property name="userDn" value="cn=manager,dc=springframework,dc=org"/>
  <property name="password" value="password"/>
</bean>

<bean id="ldapAuthProvider"
    class="org.springframework.security.ldap.authentication.LdapAuthenticationProvider">
 <constructor-arg>
   <bean class="org.springframework.security.ldap.authentication.BindAuthenticator">
     <constructor-arg ref="contextSource"/>
     <property name="userDnPatterns">
       <list><value>uid={0},ou=people</value></list>
     </property>
   </bean>
 </constructor-arg>
 <constructor-arg>
   <bean
     class="org.springframework.security.ldap.userdetails.DefaultLdapAuthoritiesPopulator">
     <constructor-arg ref="contextSource"/>
     <constructor-arg value="ou=groups"/>
     <property name="groupRoleAttribute" value="ou"/>
   </bean>
 </constructor-arg>
</bean>
                

This would set up the provider to access an LDAP server with URL ldap://monkeymachine:389/dc=springframework,dc=org. Authentication will be performed by attempting to bind with the DN uid=<user-login-name>,ou=people,dc=springframework,dc=org. After successful authentication, roles will be assigned to the user by searching under the DN ou=groups,dc=springframework,dc=org with the default filter (member=<user's-DN>). The role name will be taken from the “ou” attribute of each match.

To configure a user search object, which uses the filter (uid=<user-login-name>) for use instead of the DN-pattern (or in addition to it), you would configure the following bean

<bean id="userSearch"
    class="org.springframework.security.ldap.search.FilterBasedLdapUserSearch">
  <constructor-arg index="0" value=""/>
  <constructor-arg index="1" value="(uid={0})"/>
  <constructor-arg index="2" ref="contextSource" />
</bean> 
                

and use it by setting the BindAuthenticator bean's userSearch property. The authenticator would then call the search object to obtain the correct user's DN before attempting to bind as this user.

The net result of an authentication using LdapAuthenticationProvider is the same as a normal Spring Security authentication using the standard UserDetailsService interface. A UserDetails object is created and stored in the returned Authentication object. As with using a UserDetailsService, a common requirement is to be able to customize this implementation and add extra properties. When using LDAP, these will normally be attributes from the user entry. The creation of the UserDetails object is controlled by the provider's UserDetailsContextMapper strategy, which is responsible for mapping user objects to and from LDAP context data:

public interface UserDetailsContextMapper {
  UserDetails mapUserFromContext(DirContextOperations ctx, String username,
          Collection<GrantedAuthority> authorities);

  void mapUserToContext(UserDetails user, DirContextAdapter ctx);
}
                

Only the first method is relevant for authentication. If you provide an implementation of this interface and inject it into the LdapAuthenticationProvider, you have control over exactly how the UserDetails object is created. The first parameter is an instance of Spring LDAP's DirContextOperations which gives you access to the LDAP attributes which were loaded during authentication. The username parameter is the name used to authenticate and the final parameter is the collection of authorities loaded for the user by the configured LdapAuthoritiesPopulator.

The way the context data is loaded varies slightly depending on the type of authentication you are using. With the BindAuthenticator, the context returned from the bind operation will be used to read the attributes, otherwise the data will be read using the standard context obtained from the configured ContextSource (when a search is configured to locate the user, this will be the data returned by the search object).