Add a realm configuration for a pki realm to elasticsearch.yml under the xpack.security.authc.realms.pki namespace. If you are configuring multiple realms, you should 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:
        pki:
          pki1:
            order: 1

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:
        pki:
          pki1:
            username_pattern: "EMAILADDRESS=(.*?)(?:,|$)"

Enable client authentication on the desired network layers (transport or http).

The PKI realm relies on the TLS settings of the node’s network interface. The realm can be configured to be more restrictive than the underlying network connection - that is, it is possible to configure the node such that some connections are accepted by the network interface but then fail to be authenticated by the PKI realm. However, the reverse is not possible. The PKI realm cannot authenticate a connection that has been refused by the network interface.

In particular this means:

The relevant network interface (transport or http) must be configured to trust any certificate that is to be used within the PKI realm. However, it possible to configure the PKI realm to trust only a subset of the certificates accepted by the network interface. 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 configure the PKI realm with its own truststore, specify the truststore.path option. For example:

xpack:
  security:
    authc:
      realms:
        pki:
          pki1:
            truststore:
              path: "/path/to/pki_truststore.jks"
              password: "x-pack-test-password"

The certificate_authorities option can be used as an alternative to the truststore.path setting.

Map roles for PKI users.

You map roles for PKI users through the role mapping APIs or by using a file stored on each node. When a user authenticates against a PKI realm, the privileges for that user are the union of all privileges defined by the roles to which the user is mapped.

You identify a user by the distinguished name in their certificate. For example, the following mapping configuration maps John Doe to the user role:

Using the role-mapping API:

PUT /_security/role_mapping/users
{
  "roles" : [ "user" ],
  "rules" : { "field" : {
    "dn" : "cn=John Doe,ou=example,o=com" 
  } },
  "enabled": true
}

Or, alternatively, configured in a role-mapping file:

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

The distinguished name for a PKI user follows X.500 naming conventions which place the most specific fields (like cn or uid) at the beginning of the name, and the most general fields (like o or dc) at the end of the name. Some tools, such as openssl, may print out the subject name in a different format.

One way that you can determine the correct DN for a certificate is to use the authenticate API (use the relevant PKI certificate as the means of authentication) and inspect the metadata field in the result. The user’s distinguished name will be populated under the pki_dn key. You can also use the authenticate API to validate your role mapping.

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

The PKI realm supports authorization realms as an alternative to role mapping.