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PKI User Authentication

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PKI User Authentication

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You can configure X-Pack security to use Public Key Infrastructure (PKI) certificates to authenticate users. This requires clients to present X.509 certificates. To use PKI, you configure a PKI realm, enable client authentication on the desired network layers (transport or http), and map the Distinguished Names (DNs) from the user certificates to X-Pack security roles in the role mapping file.

You can also use a combination of PKI and username/password authentication. For example, you can enable SSL/TLS on the transport layer and define a PKI realm to require transport clients to authenticate with X.509 certificates, while still authenticating HTTP traffic using username and password credentials. You can also set xpack.security.transport.ssl.client_authentication to optional to allow clients without certificates to authenticate with other credentials.

You must enable SSL/TLS and enabled client authentication to use PKI. For more information, see Setting Up SSL/TLS on a Cluster.

PKI Realm Configuration

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Like other realms, you configure options for a pki realm under the xpack.security.authc.realms namespace in elasticsearch.yml.

To configure pki realm:

Add a realm configuration of type pki to elasticsearch.yml under the xpack.security.authc.realms namespace. At a minimum, you must set the realm type to pki. If you are configuring multiple realms, you should also explicitly set the order attribute. See PKI Realm Settings for all of the options you can set for a pki realm.

For example, the following snippet shows the most basic pki realm configuration:
```
xpack:
  security:
    authc:
      realms:
        pki1:
          type: pki
```
With this configuration, any certificate trusted by the SSL/TLS layer is accepted for authentication. The username is the common name (CN) extracted from the DN of the certificate.

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.

If you want to use something other than the CN of the DN as the username, you can specify a regex to extract the desired username. For example, the regex in the following configuration extracts the email address from the DN:
```
xpack:
  security:
    authc:
      realms:
        pki1:
          type: pki
          username_pattern: "EMAILADDRESS=(.*?)(?:,|$)"
```
You can also specify which truststore to use for authentication. This is useful when the SSL/TLS layer trusts clients with certificates that are signed by a different CA than the one that signs your users' certificates. To specify the location of the truststore, specify the truststore.path option:
```
xpack:
  security:
    authc:
      realms:
        pki1:
          type: pki
          truststore:
            path: "/path/to/pki_truststore.jks"
            password: "changeme"
```
Restart Elasticsearch.

PKI Realm Settings

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Setting	Required	Description
`type`	yes	Indicates the realm type. Must be set to `pki`.
`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`.
`username_pattern`	no	Specifies the regular expression pattern used to extract the username from the certificate DN. The first match group is used as the username. Defaults to `CN=(.*?)(?:,\|$)`.
`truststore.path`	no	The path to the truststore. Defaults to the path defined by SSL/TLS settings.
`truststore.password`	no/yes	Specifies the password for the truststore. Must be provided if `truststore.path` is set.
`truststore.algorithm`	no	Specifies the algorithm used for the truststore. Defaults to `SunX509`.
`files.role_mapping`	no	Specifies the location for the YAML role mapping configuration file. Defaults to `CONFIG_DIR/x-pack/role_mapping.yml`.

Mapping Roles for PKI Users

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You map roles for PKI users in the role mapping file stored on each node. You identify a user by the distinguished name in their certificate. For example, the following mapping configuration maps John Doe to the user role:

user: 
  - "cn=John Doe,ou=example,o=com"

	The name of a role.
	The distinguished name (DN) of a PKI user.

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

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