[role="xpack"]
[[active-directory-realm]]
=== Active Directory user authentication

You can configure {stack} {security-features} to communicate with Active
Directory to authenticate users. See <<ad-realm-configuration>>.

The {security-features} use LDAP to communicate with Active Directory, so
`active_directory` realms are similar to <<ldap-realm, `ldap` realms>>. Like
LDAP directories, Active Directory stores users and groups hierarchically. The
directory's hierarchy is built from containers such as the _organizational unit_
(`ou`), _organization_ (`o`), and _domain controller_ (`dc`).

The path to an entry is a _Distinguished Name_ (DN) that uniquely identifies a
user or group. User and group names typically have attributes such as a
_common name_ (`cn`) or _unique ID_ (`uid`). A DN is specified as a string, for
example `"cn=admin,dc=example,dc=com"` (white spaces are ignored).

The {security-features} supports only Active Directory security groups. You
cannot map distribution groups to roles.

NOTE: When you use Active Directory for authentication, the username entered by
      the user is expected to match the `sAMAccountName` or `userPrincipalName`,
      not the common name.

The Active Directory realm authenticates users using an LDAP bind request. After
authenticating the user, the realm then searches to find the user's entry in
Active Directory. Once the user has been found, the Active Directory realm then
retrieves the user's group memberships from the `tokenGroups` attribute on the
user's entry in Active Directory.

[[ad-realm-configuration]]
==== Configuring an Active Directory realm

include::configuring-active-directory-realm.asciidoc[]

[[ad-user-metadata]]
==== User metadata in Active Directory realms
When a user is authenticated via an Active Directory realm, the following
properties are populated in the user's _metadata_:

|=======================
| Field               | Description
| `ldap_dn`           | The distinguished name of the user.
| `ldap_groups`       | The distinguished name of each of the groups that were
                        resolved for the user (regardless of whether those
                        groups were mapped to a role).
|=======================

This metadata is returned in the
<<security-api-authenticate,authenticate API>> and can be used with
<<templating-role-query, templated queries>> in roles.

Additional metadata can be extracted from the Active Directory server by configuring
the `metadata` setting on the Active Directory realm.

[[ad-load-balancing]]
==== Load balancing and failover
The `load_balance.type` setting can be used at the realm level to configure how
the {security-features} should interact with multiple Active Directory servers.
Two modes of operation are supported: failover and load balancing.

See
<<load-balancing>>.

include::../securing-communications/tls-ad.asciidoc[]
