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LDAP user authentication

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LDAP user authentication

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You can configure the Elastic Stack security features to communicate with a Lightweight Directory Access Protocol (LDAP) server to authenticate users. See Configuring an LDAP realm.

LDAP stores users and groups hierarchically, similar to the way folders are grouped in a file system. An LDAP 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 ldap realm supports two modes of operation, a user search mode and a mode with specific templates for user DNs.

Mapping LDAP groups to roles

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An integral part of a realm authentication process is to resolve the roles associated with the authenticated user. Roles define the privileges a user has in the cluster.

Since with the ldap realm the users are managed externally in the LDAP server, the expectation is that their roles are managed there as well. In fact, LDAP supports the notion of groups, which often represent user roles for different systems in the organization.

The ldap realm enables you to map LDAP users to roles via their LDAP groups or other metadata. This role mapping can be configured via the add role mapping API or by using a file stored on each node. When a user authenticates with LDAP, the privileges for that user are the union of all privileges defined by the roles to which the user is mapped.

Configuring an LDAP realm

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To integrate with LDAP, you configure an ldap realm and map LDAP groups to user roles.

Determine which mode you want to use. The ldap realm supports two modes of operation, a user search mode and a mode with specific templates for user DNs.

LDAP user search is the most common mode of operation. In this mode, a specific user with permission to search the LDAP directory is used to search for the DN of the authenticating user based on the provided username and an LDAP attribute. Once found, the user is authenticated by attempting to bind to the LDAP server using the found DN and the provided password.

If your LDAP environment uses a few specific standard naming conditions for users, you can use user DN templates to configure the realm. The advantage of this method is that a search does not have to be performed to find the user DN. However, multiple bind operations might be needed to find the correct user DN.
To configure an ldap realm with user search:
1. Add a realm configuration to elasticsearch.yml under the xpack.security.authc.realms.ldap namespace. At a minimum, you must specify the url of the LDAP server, and set user_search.base_dn to the container DN where the users are searched for. If you are configuring multiple realms, you should also explicitly set the order attribute to control the order in which the realms are consulted during authentication. See LDAP realm settings for all of the options you can set for an ldap realm.
  
  For example, the following snippet shows an LDAP realm configured with a user search:
```
xpack:
  security:
    authc:
      realms:
        ldap:
          ldap1:
            order: 0
            url: "ldaps://ldap.example.com:636"
            bind_dn: "cn=ldapuser, ou=users, o=services, dc=example, dc=com"
            user_search:
              base_dn: "dc=example,dc=com"
              filter: "(cn={0})"
            group_search:
              base_dn: "dc=example,dc=com"
            files:
              role_mapping: "ES_PATH_CONF/role_mapping.yml"
            unmapped_groups_as_roles: false
```
  The password for the bind_dn user should be configured by adding the appropriate secure_bind_password setting to the Elasticsearch keystore. For example, the following command adds the password for the example realm above:
```
bin/elasticsearch-keystore add \
xpack.security.authc.realms.ldap.ldap1.secure_bind_password
```
  When you configure realms in elasticsearch.yml, only the realms you specify are used for authentication. If you also want to use the native or file realms, you must include them in the realm chain.
To configure an ldap realm with user DN templates:
1. Add a realm configuration to elasticsearch.yml in the xpack.security.authc.realms.ldap namespace. At a minimum, you must specify the url of the LDAP server, and specify at least one template with the user_dn_templates option. If you are configuring multiple realms, you should also explicitly set the order attribute to control the order in which the realms are consulted during authentication. See LDAP realm settings for all of the options you can set for an ldap realm.
  
  For example, the following snippet shows an LDAP realm configured with user DN templates:
```
xpack:
  security:
    authc:
      realms:
        ldap:
          ldap1:
            order: 0
            url: "ldaps://ldap.example.com:636"
            user_dn_templates:
              - "cn={0}, ou=users, o=marketing, dc=example, dc=com"
              - "cn={0}, ou=users, o=engineering, dc=example, dc=com"
            group_search:
              base_dn: "dc=example,dc=com"
            files:
              role_mapping: "/mnt/elasticsearch/group_to_role_mapping.yml"
            unmapped_groups_as_roles: false
```
  The bind_dn setting is not used in template mode. All LDAP operations run as the authenticating user.
(Optional) Configure how the security features interact with multiple LDAP servers.

The load_balance.type setting can be used at the realm level. The Elasticsearch security features support both failover and load balancing modes of operation. See LDAP realm settings.
(Optional) To protect passwords, encrypt communications between Elasticsearch and the LDAP server.
Restart Elasticsearch.
Map LDAP groups to roles.

The ldap realm enables you to map LDAP users to roles via their LDAP groups, or other metadata. This role mapping can be configured via the add role mapping API or by using a file stored on each node. When a user authenticates with LDAP, the privileges for that user are the union of all privileges defined by the roles to which the user is mapped.

Within a mapping definition, you specify groups using their distinguished names. For example, the following mapping configuration maps the LDAP admins group to both the monitoring and user roles, and maps the users group to the user role.

Configured via the role-mapping API:
```
PUT /_security/role_mapping/admins
{
  "roles" : [ "monitoring" , "user" ],
  "rules" : { "field" : {
    "groups" : "cn=admins,dc=example,dc=com" 
  } },
  "enabled": true
}
```
The LDAP distinguished name (DN) of the admins group.
```
PUT /_security/role_mapping/basic_users
{
  "roles" : [ "user" ],
  "rules" : { "field" : {
    "groups" : "cn=users,dc=example,dc=com" 
  } },
  "enabled": true
}
```
The LDAP distinguished name (DN) of the users group.

Or, alternatively, configured via the role-mapping file:
```
monitoring: 
  - "cn=admins,dc=example,dc=com" 
user:
  - "cn=users,dc=example,dc=com" 
  - "cn=admins,dc=example,dc=com"
```
The name of the mapped role.

The LDAP distinguished name (DN) of the admins group.

The LDAP distinguished name (DN) of the users group.

For more information, see Mapping LDAP groups to roles and Mapping users and groups to roles.

The LDAP realm supports authorization realms as an alternative to role mapping.
(Optional) Configure the metadata setting on the LDAP realm to include extra fields in the user’s metadata.

By default, ldap_dn and ldap_groups are populated in the user’s metadata. For more information, see User metadata in LDAP realms.

The example below includes the user’s common name (cn) as an additional field in their metadata.
```
xpack:
  security:
    authc:
      realms:
        ldap:
          ldap1:
            metadata: cn
```
Set up SSL to encrypt communications between Elasticsearch and LDAP. See Encrypting communications between Elasticsearch and LDAP.

User metadata in LDAP realms

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When a user is authenticated via an LDAP 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 authenticate API, and can be used with templated queries in roles.

Additional fields can be included in the user’s metadata by configuring the metadata setting on the LDAP realm. This metadata is available for use with the role mapping API or in templated role queries.

Load balancing and failover

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The load_balance.type setting can be used at the realm level to configure how the security features should interact with multiple LDAP servers. The security features support both failover and load balancing modes of operation.

See Load balancing and failover.

Encrypting communications between Elasticsearch and LDAP

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To protect the user credentials that are sent for authentication in an LDAP realm, it’s highly recommended to encrypt communications between Elasticsearch and your LDAP server. Connecting via SSL/TLS ensures that the identity of the LDAP server is authenticated before Elasticsearch transmits the user credentials and the contents of the connection are encrypted. Clients and nodes that connect via TLS to the LDAP server need to have the LDAP server’s certificate or the server’s root CA certificate installed in their keystore or truststore.

For more information, see LDAP user authentication.

Configure the realm’s TLS settings on each node to trust certificates signed by the CA that signed your LDAP server certificates. The following example demonstrates how to trust a CA certificate, cacert.pem, located within the Elasticsearch configuration directory (ES_PATH_CONF):
```
xpack:
  security:
    authc:
      realms:
        ldap:
          ldap1:
            order: 0
            url: "ldaps://ldap.example.com:636"
            ssl:
              certificate_authorities: [ "ES_PATH_CONF/cacert.pem" ]
```
The CA certificate must be a PEM encoded.

You can also specify the individual server certificates rather than the CA certificate, but this is only recommended if you have a single LDAP server or the certificates are self-signed.
Set the url attribute in the realm configuration to specify the LDAPS protocol and the secure port number. For example, url: ldaps://ldap.example.com:636.
Restart Elasticsearch.

By default, when you configure Elasticsearch to connect to an LDAP server using SSL/TLS, it attempts to verify the hostname or IP address specified with the url attribute in the realm configuration with the values in the certificate. If the values in the certificate and realm configuration do not match, Elasticsearch does not allow a connection to the LDAP server. This is done to protect against man-in-the-middle attacks. If necessary, you can disable this behavior by setting the ssl.verification_mode property to certificate.

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	The name of the mapped role.
	The LDAP distinguished name (DN) of the `admins` group.
	The LDAP distinguished name (DN) of the `users` group.