[[pki-realm-for-direct-clients]]
==== PKI authentication for clients connecting directly to {es}

To use PKI in {es}, you configure a PKI realm, enable client authentication on
the desired network layers (transport or http), and map the Distinguished Names
(DNs) from the Subject field in the user certificates to roles. You create the
mappings in a role mapping file or use the role mappings API.

TIP: You can 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.

. 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
<<ref-pki-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:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        pki:
          pki1:
            order: 1
------------------------------------------------------------

With this configuration, any certificate trusted by the {es} SSL/TLS layer is
accepted for authentication. The username is the common name (CN) extracted
from the DN in the Subject field of the end-entity certificate. This
configuration is not sufficient to permit PKI authentication to {kib};
additional steps are required.

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.

--

. Optional: If you want to use something other than the CN of the Subject DN as
the username, you can specify a regex to extract the desired username. The regex
is applied on the Subject DN.
+
--
For example, the regex in the following
configuration extracts the email address from the Subject DN:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        pki:
          pki1:
            username_pattern: "EMAILADDRESS=(.*?)(?:,|$)"
------------------------------------------------------------

NOTE: If the regex is too restrictive and does not match the Subject DN of the
client's certificate, then the realm does not authenticate the certificate.

--

. Optional: If you want the same users to also be authenticated using
certificates when they connect to {kib}, you must configure the {es} PKI realm
to allow delegation. See <<pki-realm-for-proxied-clients>>.

. Restart {es} because realm configuration is not reloaded automatically. If
you're following through with the next steps, you might wish to hold the
restart for last.

. <<configuring-tls,Enable SSL/TLS>>.

. Enable client authentication on the desired network layers (transport or http).
+
--
IMPORTANT: To use PKI when clients connect directly to {es}, you must enable
SSL/TLS with client authentication. That is to say, you must set   `xpack.security.transport.ssl.client_authentication` and
`xpack.security.http.ssl.client_authentication` to `optional` or `required`. If
the setting value is `optional`, clients without certificates can authenticate
with other credentials.

When clients connect directly to {es} and are not proxy-authenticated, 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 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.
  
For an explanation of these settings, see <<ssl-tls-settings>>.

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 is 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. The path must be located within the Elasticsearch
configuration directory (`ES_PATH_CONF`). For example:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      realms:
        pki:
          pki1:
            truststore:
              path: "pki1_truststore.jks"
------------------------------------------------------------

If the truststore is password protected, the password should be configured by
adding the appropriate `secure_password` setting to the {es} keystore.  For
example, the following command adds the password for the example realm above:

[source, shell]
------------------------------------------------------------
bin/elasticsearch-keystore add \
xpack.security.authc.realms.pki.pki1.truststore.secure_password
------------------------------------------------------------

The `certificate_authorities` option can be used as an alternative to the
`truststore.path` setting, when the certificate files are PEM formatted. The
setting accepts a list. The two options are exclusive, they cannot be both used
simultaneously.
--

. Map roles for PKI users.
+
--
You map roles for PKI users through the
<<security-role-mapping-apis,role mapping APIs>> or by using a file stored on
each node. Both configuration options are merged together. 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:

[source,console]
--------------------------------------------------
PUT /_security/role_mapping/users
{
  "roles" : [ "user" ],
  "rules" : { "field" : {
    "dn" : "cn=John Doe,ou=example,o=com" <1>
  } },
  "enabled": true
}
--------------------------------------------------

<1> The distinguished name (DN) of a PKI user.

Alternatively, use a role-mapping file. For example:

[source, yaml]
------------------------------------------------------------
user: <1>
  - "cn=John Doe,ou=example,o=com" <2>
------------------------------------------------------------
<1> The name of a role.
<2> The distinguished name (DN) of a PKI user.

The file's path defaults to `ES_PATH_CONF/role_mapping.yml`. You can specify a
different path (which must be within `ES_PATH_CONF`) by using the
`files.role_mapping` realm setting (e.g.
`xpack.security.authc.realms.pki.pki1.files.role_mapping`).

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
<<security-api-authenticate,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-roles>>.

NOTE: The PKI realm supports <<authorization_realms,authorization realms>> as an
alternative to role mapping.

--

[[pki-realm-for-proxied-clients]]
==== PKI authentication for clients connecting to {kib}

By default, the PKI realm relies on the node's network interface to perform the
SSL/TLS handshake and extract the client certificate. This behaviour requires
that clients connect directly to {es} so that their SSL connection is terminated
by the {es} node.  If SSL/TLS authentication is to be performed by {kib}, the
PKI realm must be configured to permit delegation.

Specifically, when clients presenting X.509 certificates connect to {kib},
{kib} performs the SSL/TLS authentication. {kib} then forwards the client's
certificate chain (by calling an {es} API) to have them further validated by
the PKI realms that have been configured for delegation.

To permit authentication delegation for a specific {es} PKI realm, start by
configuring the realm for the usual case, as detailed in the
<<pki-realm-for-direct-clients>> section. In this scenario, when you enable TLS,
it is mandatory that you <<tls-http,encrypt HTTP client communications>>.

You must also explicitly configure a `truststore` (or, equivalently
`certificate_authorities`) even though it is the same trust configuration that
you have configured on the network layer. The
`xpack.security.authc.token.enabled` and `delegation.enabled` settings must also
be `true`. For example:

[source, yaml]
------------------------------------------------------------
xpack:
  security:
    authc:
      token.enabled: true
      realms:
        pki:
          pki1:
            order: 1
            delegation.enabled: true
            truststore:
              path: "pki1_truststore.jks"
------------------------------------------------------------

After you restart {es}, this realm can validate delegated PKI authentication.
You must then 
{kibana-ref}/kibana-authentication.html#pki-authentication[configure {kib} to allow PKI certificate authentication].

A PKI realm with `delegation.enabled` still works unchanged for clients
connecting directly to {es}. Directly authenticated users and users that are PKI
authenticated by delegation to {kib} both follow the same
<<mapping-roles,role mapping rules>> or
<<authorization_realms,authorization realms configurations>>.

If you use the <<security-role-mapping-apis,role mapping APIs>>, however, you
can distinguish between users that are authenticated by delegation and users
that are authenticated directly. The former have the extra fields
`pki_delegated_by_user` and `pki_delegated_by_realm` in the user's metadata. In
the common setup, where authentication is delegated to {kib}, the values of
these fields are `kibana` and `reserved`, respectively. For example, the
following role mapping rule assigns the `role_for_pki1_direct` role to all users
that have been authenticated directly by the `pki1` realm, by connecting to {es}
instead of going through {kib}:

[source,console]
--------------------------------------------------
PUT /_security/role_mapping/direct_pki_only
{
  "roles" : [ "role_for_pki1_direct" ],
  "rules" : {
    "all": [
      {
        "field": {"realm.name": "pki1"}
      },
      {
        "field": {
          "metadata.pki_delegated_by_user": null <1>
        }
      }
    ]
  },
  "enabled": true
}
--------------------------------------------------

<1> If this metadata field is set (that is to say, it is *not* `null`), the user
has been authenticated in the delegation scenario.
