The PKI realm requires that SSL/TLS be enabled and client authentication also be enabled on the desired network layers (http and/or transport). It is possible to enable SSL/TLS and client authentication on only one network layer and use PKI authentication for that layer; for example, enabling SSL/TLS and client authentication on the transport layer with a PKI realm defined would allow for transport clients to authenticate with X.509 certificates while HTTP traffic would still authenticate using username and password authentication. The PKI realm supports a client authentication setting of either required or optional; required forces all clients to present a certificate, while optional enables clients without certificates to authenticate with other credentials. For SSL/TLS configuration details, please see SSL/TLS settings.

Like all realms, the pki realm is configured under the shield.authc.realms settings namespace in the elasticsearch.yml file. The following snippet shows an example of the most basic configuration:

shield:
  authc:
    realms:
      pki1:
        type: pki

In the above configuration, any certificate trusted by the SSL/TLS layer will be accepted for authentication. The username will be the common name (CN) extracted from the DN of the certificate. If the username that should be used is something other than the CN of the DN, a regex can be provided to extract the value desired for the username. The following example will extract the email address from the DN:

shield:
  authc:
    realms:
      pki1:
        type: pki
        username_pattern: "EMAILADDRESS=(.*?)(?:,|$)"

The PKI realm also provides configuration options to specify a specific truststore for authentication, which is useful when the SSL/TLS layer trusts clients with certificates that are signed by a different CA than the one that signs the certificates for client authentication. The following example shows such a configuration:

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