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LDAP User Authentication

You can configure Shield to communicate with a Lightweight Directory Access Protocol (LDAP) directory to authenticate users. To integrate with LDAP, you configure an LDAP realm and assign LDAP groups to Shield roles in the role mapping file.

To protect passwords, communications between Shield and the LDAP server should be encrypted using SSL/TLS. Clients and nodes that connect via SSL/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 about installing certificates, see Setting Up SSL.

Configuring an LDAP Realm

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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 space is ignored.

The LDAP realm supports two modes of operation, a user search mode and a mode with specific templates for user DNs. See LDAP Realm Settings for all of the options you can set for an LDAP realm.

Configuring an LDAP Realm with User Search [1.1.0] Added in 1.1.0.

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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 user DN based on the username and an LDAP attribute.

To configure an LDAP Realm with User Search:

Add a realm configuration of type ldap to elasticsearch.yml in the shield.authc.realms namespace. At a minimum, you must set the realm type to ldap, specify the url of the LDAP server, and specify the container DN to search for users with the user_search.base_dn 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 a user search:
```
shield:
  authc:
    realms:
      ldap1:
        type: ldap
        order: 0
        url: "ldaps://ldap.example.com:636"
        bind_dn: "cn=ldapuser, ou=users, o=services, dc=example, dc=com"
        bind_password: changeme
        user_search:
          base_dn: "dc=example,dc=com"
          attribute: cn
        group_search:
          base_dn: "dc=example,dc=com"
        files:
          role_mapping: "CONFIG_DIR/shield/role_mapping.yml"
        unmapped_groups_as_roles: false
```
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.
Restart Elasticsearch

Configuring an LDAP Realm with User DN Templates

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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:

Add a realm configuration of type ldap to elasticsearch.yml in the shield.authc.realms namespace. At a minimum, you must set the realm type to ldap, 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:
```
shield:
  authc:
    realms:
      ldap1:
        type: ldap
        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
```

LDAP Load Balancing and Failover [2.3.0] Added in 2.3.0.

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

Table 1. Load Balancing and Failover Types

Type	Description
`failover`	The URLs specified are used in the order that they are specified. The first server that can be connected to will be used for all subsequent connections. If a connection to that server fails then the next server that a connection can be established to will be used for subsequent connections.
`dns_failover`	In this mode of operation, only a single URL may be specified. This URL must contain a DNS name. The system will be queried for all IP addresses that correspond to this DNS name. Connections to the LDAP server will always be tried in the order in which they were retrieved. This differs from `failover` in that there is no reordering of the list and if a server has failed at the beginning of the list, it will still be tried for each subsequent connection.
`round_robin`	Connections will continuously iterate through the list of provided URLs. If a server is unavailable, iterating through the list of URLs will continue until a successful connection is made.
`dns_round_robin`	In this mode of operation, only a single URL may be specified. This URL must contain a DNS name. The system will be queried for all IP addresses that correspond to this DNS name. Connections will continuously iterate through the list of addresses. If a server is unavailable, iterating through the list of URLs will continue until a successful connection is made.

LDAP Realm Settings

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Table 2. Common LDAP Realm Settings

Setting	Required	Description
`type`	yes	Indicates the realm type. Must be set to `ldap`.
`order`	no	Indicates the priority of this realm within the realm chain. Realms with a lower order are consulted first. Although not required, we recommend explicitly setting this value when you configure multiple realms. Defaults to `Integer.MAX_VALUE`.
`enabled`	no	Indicates whether this realm is enabled or disabled. Enables you to disable a realm without removing its configuration. Defaults to `true`.
`url`	yes	Specifies one or more LDAP URLs of the form of `ldap[s]://<server>:<port>`. Multiple URLs can be defined using a comma separated value or array syntax: `[ "ldaps://server1:636", "ldaps://server2:636" ]`. ldaps and ldap URLs cannot be mixed in the same realm.
`load_balance.type`	no	The behavior to use when there are multiple LDAP URLs defined. For supported values see LDAP load balancing and failover types.
`load_balance.cache_ttl`	no	When using `dns_failover` or `dns_round_robin` as the load balancing type, this setting controls the amount of time to cache DNS lookups. Defaults to `1h`.
`user_group_attribute`	no	Specifies the attribute to examine on the user for group membership. The default is `memberOf`. This setting will be ignored if any `group_search` settings are specified.
`group_search.base_dn`	no	Specifies a container DN to search for groups in which the user has membership. When this element is absent, Shield searches for the attribute specified by `user_group_attribute` set on the user to determine group membership.
`group_search.scope`	no	Specifies whether the group search should be `sub_tree`, `one_level` or `base`. `one_level` only searches objects directly contained within the `base_dn`. The default `sub_tree` searches all objects contained under `base_dn`. `base` specifies that the `base_dn` is a group object, and that it is the only group considered.
`group_search.filter`	no	Specifies a filter to use to lookup a group. If not set, the realm searches for `group`, `groupOfNames`, or `groupOfUniqueNames`, with the attributes `member` or `memberOf`. Any instance of `{0}` in the filter is replaced by the user attribute defined in `group_search.user_attribute`
`group_search.user_attribute`	no	Specifies the user attribute that is fetched and provided as a parameter to the filter. If not set, the user DN is passed to the filter.
`unmapped_groups_as_roles`	no	Specifies whether the names of any unmapped LDAP groups should be used as role names and assigned to the user. Defaults to `false`.
`timeout.tcp_connect`	no	Specifies the TCP connect timeout period for establishing an LDAP connection. An `s` at the end indicates seconds, or `ms` indicates milliseconds. Defaults to `5s` (5 seconds).
`timeout.tcp_read`	no	Specifies the TCP read timeout period after establishing an LDAP connection. An `s` at the end indicates seconds, or `ms` indicates milliseconds. Defaults to `5s` (5 seconds).
`timeout.ldap_search`	no	Specifies the LDAP Server enforced timeout period for an LDAP search. An `s` at the end indicates seconds, or `ms` indicates milliseconds. Defaults to `5s` (5 seconds).
`files.role_mapping`	no	Specifies the path and file name for the YAML role mapping configuration file. Defaults to `ES_HOME/config/shield/role_mapping.yml`.
`follow_referrals`	no	Specifies whether Shield should follow referrals returned by the LDAP server. Referrals are URLs returned by the server that are to be used to continue the LDAP operation (e.g. search). Defaults to `true`.
`hostname_verification`	no	Specifies whether hostname verification is performed when connecting to an LDAP server. When `true`, the hostname or IP address used in the `url` must match one of the names in the certificate or the connection will not be allowed. Due to its potential security impact, `hostname_verification` is not exposed via the nodes info API. Defaults to `true`.
`cache.ttl`	no	Specifies the time-to-live for cached user entries. A user’s credentials are cached for this period of time. Specify the time period using the standard Elasticsearch time units. Defaults to `20m`.
`cache.max_users`	no	Specifies the maximum number of user entries that can be stored in the cache at one time. Defaults to 100,000.
`cache.hash_algo`	no	Specifies the hashing algorithm that is used for the cached user credentials. See Cache hash algorithms for the possible values. (Expert Setting)

Table 3. User Template LDAP Realm Settings

Setting	Required	Description
`user_dn_templates`	yes	Specifies the DN template that replaces the user name with the string `{0}`. This element is multivalued, allowing for multiple user contexts.

Table 4. User Search LDAP Realm Settings [1.1.0] Added in 1.1.0.

Setting	Required	Description
`bind_dn`	no	The DN of the user that is used to bind to the LDAP and perform searches. If not specified, an anonymous bind is attempted. Due to its potential security impact, `hostname_verification` is not exposed via the nodes info API.
`bind_password`	no	The password for the user that is used to bind to the LDAP. Due to its potential security impact, `hostname_verification` is not exposed via the nodes info API.
`user_search.base_dn`	yes	Specifies a container DN to search for users.
`user_search.scope`	no	The scope of the user search. Valid values are `sub_tree`, `one_level` or `base`. `one_level` only searches objects directly contained within the `base_dn`. `sub_tree` searches all objects contained under `base_dn`. `base` specifies that the `base_dn` is the user object, and that it is the only user considered. Defaults to `sub_tree`.
`user_search.attribute`	no	Specifies the attribute to match with the username presented to Shield. Defaults to `uid`.
`user_search.pool.size`	no	Specifies the maximum number of connections to the LDAP server to allow in the connection pool. Defaults to `20`.
`user_search.pool.initial_size`	no	The initial number of connections to create to the LDAP server on startup. Defaults to `5`.
`user_search.pool.health_check.enabled`	no	Enables or disables a health check on LDAP connections in the connection pool. Connections are checked in the background at the specified interval. Defaults to `true`.
`user_search.pool.health_check.dn`	no	Specifies the distinguished name to retrieve as part of the health check. Defaults to the value of `bind_dn`. If `bind_dn` is not configured, you must specify a value.
`user_search.pool.health_check.interval`	no	How often to perform background checks of connections in the pool. Defaults to `60s`.

If any settings starting with user_search are specified, the user_dn_templates the settings are ignored.

Assigning LDAP Groups to Roles

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To configure privileges for LDAP users, you assign LDAP groups to roles in the role mapping 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 assigned to the set of groups that the user belongs to.

You specify groups using their distinguished names. For example, the following mapping configuration assigns the LDAP admins group both the monitoring and user roles, and assigns the user role to the users group.

monitoring: 
  - "cn=admins,dc=example,dc=com" 
user:
  - "cn=users,dc=example,dc=com" 
  - "cn=admins,dc=example,dc=com"

	The name of a role defined in `roles.yml`.
	The distinguished name of the `admins` group.
	The distinguished name of the `users` group.

For more information, see Mapping Users and Groups to Roles.

Encrypting Communications Between Shield and LDAP with SSL/TLS

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You should encrypt communications between Shield and your LDAP server to protect the user credentials that are sent to for authentication. Connecting via SSL/TLS ensures that the identity of the LDAP server is authenticated before Shield transmits the user credentials, and the user names and passwords are encrypted in transit.

To encrypt communications between Shield and your LDAP server:

Configure each node to trust certificates signed by the CA that signed your LDAP server certificates. For example, the following command imports cacert.pem into node01’s keystore. (For information about using truststores, see Configuring a Separate Truststore.)
```
cd CONFIG_DIR/shield
keytool -importcert -keystore node01.jks -file cacert.pem -alias ldap_ca
```
The CA cert must be a PEM encoded certificate.
You can also import the individual server certificates rather than the CA certificate, but this is only recommended if you have a single LDAP server. You can fetch the LDAP server certificate with openssl. For example, the following command gets the certificate for ldap.example.com and stores it locally in ldap.crt.
```
echo | openssl s_client -connect ldap.example.com:636 2>/dev/null | openssl x509 > ldap.crt
```
If you are using an older version of openssl you might need to use use the -host and -port options rather than the -connect option.

If you haven’t already configured the path to the node’s keystore or truststore in elasticsearch.yml, set the shield.ssl.keystore.path or shield.ssl.truststore.path attributes. For example:

shield.ssl.keystore.path:          /home/es/config/shield/node01.jks 
shield.ssl.keystore.password:      myPass 
shield.ssl.keystore.key_password:  myKeyPass

	The full path to the node keystore file. This must be a location within the Elasticsearch configuration directory.
	The password used to access the keystore.
	The password used to access the certificate. This is only required if you specified a separate certificate password when generating the certificate.

For more information, see Enabling SSL/TLS in the Node Configuration.

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 to pick up the changes to elasticsearch.yml.

By default, when you configure Shield to connect to an LDAP server using SSL/TLS, Shield 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, Shield 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 hostname_verification property to false. hostname_verification is considered to be a sensitive setting and is not exposed via nodes info API.

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