[[servlet-authentication-ldap]]
= LDAP Authentication

LDAP is often used by organizations as a central repository for user information and as an authentication service.
It can also be used to store the role information for application users.

Spring Security's LDAP based authentication is used by Spring Security when it is configured to <<servlet-authentication-unpwd-input,accept a username/password>> for authentication.
However, despite leveraging a username/password for authentication it does not integrate using `UserDetailsService` because in <<servlet-authentication-ldap-bind,bind authentication>> the LDAP server does not return the password so the application cannot perform validation of the password.

There are many different scenarios for how an LDAP server may be configured so Spring Security's LDAP provider is fully configurable.
It uses separate strategy interfaces for authentication and role retrieval and provides default implementations which can be configured to handle a wide range of situations.

[[servlet-authentication-ldap-prerequisites]]
== Prerequisites

You should be familiar with LDAP before trying to use it with Spring Security.
The following link provides a good introduction to the concepts involved and a guide to setting up a directory using the free LDAP server OpenLDAP: https://www.zytrax.com/books/ldap/.
Some familiarity with the JNDI APIs used to access LDAP from Java may also be useful.
We don't use any third-party LDAP libraries (Mozilla, JLDAP etc.) in the LDAP provider, but extensive use is made of Spring LDAP, so some familiarity with that project may be useful if you plan on adding your own customizations.

When using LDAP authentication, it is important to ensure that you configure LDAP connection pooling properly.
If you are unfamiliar with how to do this, you can refer to the https://docs.oracle.com/javase/jndi/tutorial/ldap/connect/config.html[Java LDAP documentation].


// FIXME:
// ldap server
//	embedded (both java and xml)
//	external
// authentication
//	bind
//	password
//	roles
//	search, etc (other APIs)

[[servlet-authentication-ldap-embedded]]
== Setting up an Embedded LDAP Server

The first thing you will need to do is to ensure that you have an LDAP Server to point your configuration to.
For simplicity, it often best to start with an embedded LDAP Server.
Spring Security supports using either:

* <<servlet-authentication-ldap-unboundid>>
* <<servlet-authentication-ldap-apacheds>>

In the samples below, we expose the following as `users.ldif` as a classpath resource to initialize the embedded LDAP server with the users `user` and `admin` both of which have a password of `password`.

.users.ldif
[source,ldif]
----
dn: ou=groups,dc=springframework,dc=org
objectclass: top
objectclass: organizationalUnit
ou: groups

dn: ou=people,dc=springframework,dc=org
objectclass: top
objectclass: organizationalUnit
ou: people

dn: uid=admin,ou=people,dc=springframework,dc=org
objectclass: top
objectclass: person
objectclass: organizationalPerson
objectclass: inetOrgPerson
cn: Rod Johnson
sn: Johnson
uid: admin
userPassword: password

dn: uid=user,ou=people,dc=springframework,dc=org
objectclass: top
objectclass: person
objectclass: organizationalPerson
objectclass: inetOrgPerson
cn: Dianne Emu
sn: Emu
uid: user
userPassword: password

dn: cn=user,ou=groups,dc=springframework,dc=org
objectclass: top
objectclass: groupOfNames
cn: user
uniqueMember: uid=admin,ou=people,dc=springframework,dc=org
uniqueMember: uid=user,ou=people,dc=springframework,dc=org

dn: cn=admin,ou=groups,dc=springframework,dc=org
objectclass: top
objectclass: groupOfNames
cn: admin
uniqueMember: uid=admin,ou=people,dc=springframework,dc=org
----

[[servlet-authentication-ldap-unboundid]]
=== Embedded UnboundID Server

If you wish to use https://ldap.com/unboundid-ldap-sdk-for-java/[UnboundID], then specify the following dependencies:

.UnboundID Dependencies
====
.Maven
[source,xml,role="primary",subs="verbatim,attributes"]
----
<dependency>
	<groupId>com.unboundid</groupId>
	<artifactId>unboundid-ldapsdk</artifactId>
	<version>{unboundid-ldapsdk-version}</version>
	<scope>runtime</scope>
</dependency>
----

.Gradle
[source,groovy,role="secondary",subs="verbatim,attributes"]
----
depenendencies {
	runtimeOnly "com.unboundid:unboundid-ldapsdk:{unboundid-ldapsdk-version}"
}
----
====

You can then configure the Embedded LDAP Server

.Embedded LDAP Server Configuration
====
.Java
[source,java,role="primary"]
----
@Bean
UnboundIdContainer ldapContainer() {
	return new UnboundIdContainer("dc=springframework,dc=org",
				"classpath:users.ldif");
}
----

.XML
[source,xml,role="secondary"]
----
<b:bean class="org.springframework.security.ldap.server.UnboundIdContainer"
	c:defaultPartitionSuffix="dc=springframework,dc=org"
	c:ldif="classpath:users.ldif"/>
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun ldapContainer(): UnboundIdContainer {
    return UnboundIdContainer("dc=springframework,dc=org","classpath:users.ldif")
}
----
====

[[servlet-authentication-ldap-apacheds]]
=== Embedded ApacheDS Server

[NOTE]
====
Spring Security uses ApacheDS 1.x which is no longer maintained.
Unfortunately, ApacheDS 2.x has only released milestone versions with no stable release.
Once a stable release of ApacheDS 2.x is available, we will consider updating.
====

If you wish to use https://directory.apache.org/apacheds/[Apache DS], then specify the following dependencies:

.ApacheDS Dependencies
====
.Maven
[source,xml,role="primary",subs="+attributes"]
----
<dependency>
	<groupId>org.apache.directory.server</groupId>
	<artifactId>apacheds-core</artifactId>
	<version>{apacheds-core-version}</version>
	<scope>runtime</scope>
</dependency>
<dependency>
	<groupId>org.apache.directory.server</groupId>
	<artifactId>apacheds-server-jndi</artifactId>
	<version>{apacheds-core-version}</version>
	<scope>runtime</scope>
</dependency>
----

.Gradle
[source,groovy,role="secondary",subs="+attributes"]
----
depenendencies {
	runtimeOnly "org.apache.directory.server:apacheds-core:{apacheds-core-version}"
	runtimeOnly "org.apache.directory.server:apacheds-server-jndi:{apacheds-core-version}"
}
----
====

You can then configure the Embedded LDAP Server

.Embedded LDAP Server Configuration
====
.Java
[source,java,role="primary"]
----
@Bean
ApacheDSContainer ldapContainer() {
	return new ApacheDSContainer("dc=springframework,dc=org",
				"classpath:users.ldif");
}
----

.XML
[source,xml,role="secondary"]
----
<b:bean class="org.springframework.security.ldap.server.ApacheDSContainer"
	c:defaultPartitionSuffix="dc=springframework,dc=org"
	c:ldif="classpath:users.ldif"/>
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun ldapContainer(): ApacheDSContainer {
    return ApacheDSContainer("dc=springframework,dc=org", "classpath:users.ldif")
}
----
====

[[servlet-authentication-ldap-contextsource]]
== LDAP ContextSource

Once you have an LDAP Server to point your configuration to, you need configure Spring Security to point to an LDAP server that should be used to authenticate users.
This is done by creating an LDAP `ContextSource`, which is the equivalent of a JDBC `DataSource`.

.LDAP Context Source
====
.Java
[source,java,role="primary"]
----
ContextSource contextSource(UnboundIdContainer container) {
	return new DefaultSpringSecurityContextSource("ldap://localhost:53389/dc=springframework,dc=org");
}
----

.XML
[source,xml,role="secondary"]
----
<ldap-server
	url="ldap://localhost:53389/dc=springframework,dc=org" />
----

.Kotlin
[source,kotlin,role="secondary"]
----
fun contextSource(container: UnboundIdContainer): ContextSource {
    return DefaultSpringSecurityContextSource("ldap://localhost:53389/dc=springframework,dc=org")
}
----
====

[[servlet-authentication-ldap-authentication]]
== Authentication

Spring Security's LDAP support does not use the <<servlet-authentication-userdetailsservice>> because LDAP bind authentication does not allow clients to read the password or even a hashed version of the password.
This means there is no way a password to be read and then authenticated by Spring Security.

For this reason, LDAP support is implemented using the `LdapAuthenticator` interface.
The `LdapAuthenticator` 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 two `LdapAuthenticator` implementations supplied with Spring Security:

* <<servlet-authentication-ldap-bind>>
* <<servlet-authentication-ldap-pwd>>

[[servlet-authentication-ldap-bind]]
== Using Bind Authentication

https://ldap.com/the-ldap-bind-operation/[Bind Authentication] is the most common mechanism for authenticating users with LDAP.
In bind authentication the users credentials (i.e. username/password) are submitted to the LDAP server which authenticates them.
The advantage to using bind authentication is that the user's secrets (i.e. password) do not need to be exposed to clients which helps to protect them from leaking.


An example of bind authentication configuration can be found below.

.Bind Authentication
====
.Java
[source,java,role="primary",attrs="-attributes"]
----
@Bean
BindAuthenticator authenticator(BaseLdapPathContextSource contextSource) {
	BindAuthenticator authenticator = new BindAuthenticator(contextSource);
	authenticator.setUserDnPatterns(new String[] { "uid={0},ou=people" });
	return authenticator;
}

@Bean
LdapAuthenticationProvider authenticationProvider(LdapAuthenticator authenticator) {
	return new LdapAuthenticationProvider(authenticator);
}
----

.XML
[source,xml,role="secondary",attrs="-attributes"]
----
<ldap-authentication-provider
	user-dn-pattern="uid={0},ou=people"/>
----

.Kotlin
[source,kotlin,role="secondary",attrs="-attributes"]
----
@Bean
fun authenticator(contextSource: BaseLdapPathContextSource): BindAuthenticator {
    val authenticator = BindAuthenticator(contextSource)
    authenticator.setUserDnPatterns(arrayOf("uid={0},ou=people"))
    return authenticator
}

@Bean
fun authenticationProvider(authenticator: LdapAuthenticator): LdapAuthenticationProvider {
    return LdapAuthenticationProvider(authenticator)
}
----
====

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:

.Bind Authentication with Search Filter
====
.Java
[source,java,role="primary",attrs="-attributes"]
----
@Bean
BindAuthenticator authenticator(BaseLdapPathContextSource contextSource) {
	String searchBase = "ou=people";
	String filter = "(uid={0})";
	FilterBasedLdapUserSearch search =
		new FilterBasedLdapUserSearch(searchBase, filter, contextSource);
	BindAuthenticator authenticator = new BindAuthenticator(contextSource);
	authenticator.setUserSearch(search);
	return authenticator;
}

@Bean
LdapAuthenticationProvider authenticationProvider(LdapAuthenticator authenticator) {
	return new LdapAuthenticationProvider(authenticator);
}
----

.XML
[source,xml,role="secondary",attrs="-attributes"]
----
<ldap-authentication-provider
		user-search-filter="(uid={0})"
	user-search-base="ou=people"/>
----

.Kotlin
[source,kotlin,role="secondary",attrs="-attributes"]
----
@Bean
fun authenticator(contextSource: BaseLdapPathContextSource): BindAuthenticator {
    val searchBase = "ou=people"
    val filter = "(uid={0})"
    val search = FilterBasedLdapUserSearch(searchBase, filter, contextSource)
    val authenticator = BindAuthenticator(contextSource)
    authenticator.setUserSearch(search)
    return authenticator
}

@Bean
fun authenticationProvider(authenticator: LdapAuthenticator): LdapAuthenticationProvider {
    return LdapAuthenticationProvider(authenticator)
}
----
====

If used with the `ContextSource` <<servlet-authentication-ldap-contextsource,definition above>>, this would perform a search under the DN `ou=people,dc=springframework,dc=org` using `+(uid={0})+` as a filter.
Again the user login name is substituted for the parameter in the filter name, so it will search for an entry with the `uid` attribute equal to the user name.
If a user search base isn't supplied, the search will be performed from the root.

[[servlet-authentication-ldap-pwd]]
== Using Password Authentication

Password comparison is when the password supplied by the user is compared with the one stored in the repository.
This can either be done by retrieving the value of the password attribute and checking it locally or by performing an LDAP "compare" operation, where the supplied password is passed to the server for comparison and the real password value is never retrieved.
An LDAP compare cannot be done when the password is properly hashed with a random salt.

.Minimal Password Compare Configuration
====
.Java
[source,java,role="primary"]
----
@Bean
PasswordComparisonAuthenticator authenticator(BaseLdapPathContextSource contextSource) {
	return new PasswordComparisonAuthenticator(contextSource);
}

@Bean
LdapAuthenticationProvider authenticationProvider(LdapAuthenticator authenticator) {
	return new LdapAuthenticationProvider(authenticator);
}
----

.XML
[source,xml,role="secondary",attrs="-attributes"]
----
<ldap-authentication-provider
		user-dn-pattern="uid={0},ou=people">
	<password-compare />
</ldap-authentication-provider>
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun authenticator(contextSource: BaseLdapPathContextSource): PasswordComparisonAuthenticator {
    return PasswordComparisonAuthenticator(contextSource)
}

@Bean
fun authenticationProvider(authenticator: LdapAuthenticator): LdapAuthenticationProvider {
    return LdapAuthenticationProvider(authenticator)
}
----
====

A more advanced configuration with some customizations can be found below.

.Password Compare Configuration
====
.Java
[source,java,role="primary"]
----
@Bean
PasswordComparisonAuthenticator authenticator(BaseLdapPathContextSource contextSource) {
	PasswordComparisonAuthenticator authenticator =
		new PasswordComparisonAuthenticator(contextSource);
	authenticator.setPasswordAttributeName("pwd"); // <1>
	authenticator.setPasswordEncoder(new BCryptPasswordEncoder()); // <2>
	return authenticator;
}

@Bean
LdapAuthenticationProvider authenticationProvider(LdapAuthenticator authenticator) {
	return new LdapAuthenticationProvider(authenticator);
}
----

.XML
[source,xml,role="secondary",attrs="-attributes"]
----
<ldap-authentication-provider
		user-dn-pattern="uid={0},ou=people">
	<password-compare password-attribute="pwd"> <!--1-->
		<password-encoder ref="passwordEncoder" /> <!--2-->
	</password-compare>
</ldap-authentication-provider>
<b:bean id="passwordEncoder"
	class="org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder" />
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun authenticator(contextSource: BaseLdapPathContextSource): PasswordComparisonAuthenticator {
    val authenticator = PasswordComparisonAuthenticator(contextSource)
    authenticator.setPasswordAttributeName("pwd") // <1>
    authenticator.setPasswordEncoder(BCryptPasswordEncoder()) // <2>
    return authenticator
}

@Bean
fun authenticationProvider(authenticator: LdapAuthenticator): LdapAuthenticationProvider {
    return LdapAuthenticationProvider(authenticator)
}
----
====

<1> Specify the password attribute as `pwd`
<2> Use `BCryptPasswordEncoder`


== LdapAuthoritiesPopulator

Spring Security's `LdapAuthoritiesPopulator` is used to determine what authorites are returned for the user.

.LdapAuthoritiesPopulator Configuration
====
.Java
[source,java,role="primary",attrs="-attributes"]
----
@Bean
LdapAuthoritiesPopulator authorities(BaseLdapPathContextSource contextSource) {
	String groupSearchBase = "";
	DefaultLdapAuthoritiesPopulator authorities =
		new DefaultLdapAuthoritiesPopulator(contextSource, groupSearchBase);
	authorities.setGroupSearchFilter("member={0}");
	return authorities;
}

@Bean
LdapAuthenticationProvider authenticationProvider(LdapAuthenticator authenticator, LdapAuthoritiesPopulator authorities) {
	return new LdapAuthenticationProvider(authenticator, authorities);
}
----

.XML
[source,xml,role="secondary",attrs="-attributes"]
----
<ldap-authentication-provider
	user-dn-pattern="uid={0},ou=people"
	group-search-filter="member={0}"/>
----

.Kotlin
[source,kotlin,role="secondary",attrs="-attributes"]
----
@Bean
fun authorities(contextSource: BaseLdapPathContextSource): LdapAuthoritiesPopulator {
    val groupSearchBase = ""
    val authorities = DefaultLdapAuthoritiesPopulator(contextSource, groupSearchBase)
    authorities.setGroupSearchFilter("member={0}")
    return authorities
}

@Bean
fun authenticationProvider(authenticator: LdapAuthenticator, authorities: LdapAuthoritiesPopulator): LdapAuthenticationProvider {
    return LdapAuthenticationProvider(authenticator, authorities)
}
----
====

== Active Directory

Active Directory supports its own non-standard authentication options, and the normal usage pattern doesn't fit too cleanly with the standard `LdapAuthenticationProvider`.
Typically authentication is performed using the domain username (in the form `user@domain`), rather than using an LDAP distinguished name.
To make this easier, Spring Security has an authentication provider which is customized for a typical Active Directory setup.

Configuring `ActiveDirectoryLdapAuthenticationProvider` is quite straightforward.
You just need to supply the domain name and an LDAP URL supplying the address of the server footnote:[It is also possible to obtain the server's IP address using a DNS lookup.
This is not currently supported, but hopefully will be in a future version.].
An example configuration can be seen below:

.Example Active Directory Configuration
====
.Java
[source,java,role="primary"]
----
@Bean
ActiveDirectoryLdapAuthenticationProvider authenticationProvider() {
	return new ActiveDirectoryLdapAuthenticationProvider("example.com", "ldap://company.example.com/");
}
----

.XML
[source,xml,role="secondary"]
----
<bean id="authenticationProvider"
        class="org.springframework.security.ldap.authentication.ad.ActiveDirectoryLdapAuthenticationProvider">
	<constructor-arg value="example.com" />
	<constructor-arg value="ldap://company.example.com/" />
</bean>
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Bean
fun authenticationProvider(): ActiveDirectoryLdapAuthenticationProvider {
    return ActiveDirectoryLdapAuthenticationProvider("example.com", "ldap://company.example.com/")
}
----
====
