PKI User Authentication

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.

Important

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

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

To configure pki realm:

  1. 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.

    Important

    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=(.*?)(?:,|$)"
  2. Restart Elasticsearch.

PKI and SSL Settings

The PKI realm relies on the SSL settings of the node’s network interface (transport or http). 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 transport or http interface must request client certificates by setting client_authentication to optional or required.
  • The interface must trust the certificate that is presented by the client by configuring either the truststore or certificate_authorities paths, or by setting verification_mode to none.
  • The protocols supported by the interface must be compatible with those used by the client.

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 as below:

xpack:
  security:
    authc:
      realms:
        pki1:
          type: pki
          truststore:
            path: "/path/to/pki_truststore.jks"
            password: "changeme"

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

PKI Realm Settings

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=(.*?)(?:,|$).

certificate_authorities

no

List of paths to the PEM encoded certificate files that should be trusted. This setting may not be used with truststore.path.

truststore.path

no

The path to the truststore. Defaults to the path defined by SSL/TLS settings. This setting may not be used with certificate_authorities.

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

You map roles for PKI users through the role-mapping API, 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 _xpack/security/role_mapping/users
{
  "roles" : [ "user" ],
  "rules" : { "field" : {
    "dn" : "cn=John Doe,ou=example,o=com" 
  } },
  "enabled": true
}

The distinguished name (DN) of a PKI user.

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

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

The name of a role.

The distinguished name (DN) of a PKI user.

The disinguished 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.