[role="xpack"]
[[jwt-auth-realm]]
=== JWT authentication

{es} can be configured to trust JSON Web Tokens (JWTs) issued from an external service
as bearer tokens for authentication.

When a JWT realm is used to authenticate with {es}, a distinction is made
between the _client_ that is connecting to {es}, and the _user_ on whose behalf
the request should run. The JWT authenticates the user, and a separate credential
authenticates the client.

The JWT realm supports two token types, `id_token` (the default) and `access_token`.
They are designed to work for the following two scenarios, respectively:

1. `id_token` - An application authenticates and identifies a user with an authentication flow,
e.g. OpenID Connect (OIDC), and then accesses {es} on behalf of the authenticated user using
a JSON Web Token (JWT) conforming to OIDC ID Token specification.
2. `access_token` - An application accesses {es} using its own identity, encoded as a JWT,
e.g. The application authenticates itself to a central identity platform using an
OAuth2 Client Credentials Flow and then uses the resulting JWT-based access token to connect to {es}.

NOTE: A single JWT realm can only work with a single token type. To handle both token types,
you must configure at least two JWT realms. You should choose the token type carefully based
on the use case because it impacts on how validations are performed.

The JWT realm validates the incoming JWT based on its configured token type.
JSON Web Tokens (JWT) of both types must contain the following 5 pieces of information.
While ID Tokens, based on the OIDC specification, have strict rules for what claims should provide these information,
access tokens allow some claims to be configurable.

[cols="3",frame=all]
|====
h|             2+^h| Claims
h| Information     | ID Token   | Access Token
 | Issuer          | `iss`      | `iss`
 | Subject         | `sub`      | Defaults to `sub`, but can fall back to another claim if `sub` does not exist
 | Audiences       | `aud`      | Defaults to `aud`, but can fall back to another claim if `aud` does not exist
 | Issue Time      | `iat`      | `iat`
 | Expiration Time | `exp`      | `exp`
|====

In addition, {es} also validates `nbf` and `auth_time` claims for ID Tokens if these claims are present.
But these claims are ignored for access tokens.

Overall, the access token type has more relaxed validation rules and is suitable for more generic JWTs,
including self-signed ones.

[[jwt-realm-oidc]]
==== ID Tokens from OIDC workflows
JWT authentication in {es} is derived from OIDC user workflows, where different
tokens can be issued by an OIDC Provider (OP), including ID Tokens.
ID Tokens from an OIDC provider are well-defined JSON Web Tokens (JWT) and should be always compatible with
a JWT realm of the `id_token` token type. The subject claim of an ID token represents the end-user.
This means that ID tokens will generally have many allowed subjects.
Therefore, a JWT realm of `id_token` token type does _not_ mandate the `allowed_subjects`
(or `allowed_subject_patterns`) validation.

NOTE: Because JWTs are obtained external to {es}, you can define a custom workflow
instead of using the OIDC workflow. However, the JWT format must still be JSON
Web Signature (JWS). The JWS header and JWS signature are validated using OIDC
ID token validation rules.

{es} supports a separate <<oidc-realm,OpenID Connect realm>>. It is preferred for any
use case where {es} can act as an OIDC RP. The OIDC realm is the only supported
way to enable OIDC authentication in {kib}.

TIP: Users authenticating with a JWT realm can optionally impersonate another user
with the <<run-as-privilege,`run_as`>> feature. See also <<jwt-realm-runas>>.

[[jwt-realm-oauth2]]
==== Access Tokens
A common method to obtain access tokens is with the OAuth2 Client Credentials Flow.
A typical usage of this flow is for an application to get a credential for itself.
This is the use case that the `access_token` token type is designed for.
It is likely that this application also obtains ID Tokens for its end-users.
To prevent end-user ID Tokens being used to authenticate with the JWT realm configured
for the application, we mandate `allowed_subjects` or `allowed_subject_patterns`
validation when a JWT realm has token type `access_token`.

NOTE: Not every access token is formatted as a JSON Web Token (JWT).
For it to be compatible with the JWT realm, it must at least use the JWT format and satisfies
relevant requirements in the above table.


[[jwt-realm-configuration]]
==== Configure {es} to use a JWT realm

To use JWT authentication, create the realm in the `elasticsearch.yml` file
to configure it within the {es} authentication chain.

The JWT realm has a few mandatory settings, plus optional settings that are
described in <<ref-jwt-settings,JWT realm settings>>.

NOTE: Client authentication is enabled by default for the JWT realms. Disabling
client authentication is possible, but strongly discouraged.

. Add your JWT realm to the `elasticsearch.yml` file. The following example
includes the most common settings, which are not intended for every use case:
+
--
[source,yaml]
----
xpack.security.authc.realms.jwt.jwt1:
  order: 3
  token_type: id_token
  client_authentication.type: shared_secret
  allowed_issuer: "https://issuer.example.com/jwt/"
  allowed_audiences: [ "8fb85eba-979c-496c-8ae2-a57fde3f12d0" ]
  allowed_signature_algorithms: [RS256,HS256]
  pkc_jwkset_path: jwt/jwkset.json
  claims.principal: sub
----

`order`::
Specifies a realm `order` of `3`, which indicates the order in which the
configured realm is checked when authenticating a user. Realms are consulted in
ascending order, where the realm with the lowest order value is consulted first.

`token_type`::
Instructs the realm to treat and validate incoming JWTs as ID Tokens (`id_token`).

`client_authentication.type`::
Specifies the client authentication type as `shared_secret`, which means that
the client is authenticated using an HTTP request header that must match a
pre-configured secret value. The client must provide this shared secret with
every request in the `ES-Client-Authentication` header and using the
`SharedSecret` scheme. The header value must be a case-sensitive match
to the realm's `client_authentication.shared_secret`.

`allowed_issuer`::
Sets a verifiable identifier for your JWT issuer. This value is typically a
URL, UUID, or some other case-sensitive string value.

`allowed_audiences`::
Specifies a list of JWT audiences that the realm will allow.
These values are typically URLs, UUIDs, or other case-sensitive string values.

`allowed_signature_algorithms`::
Indicates that {es} should use the `RS256` or `HS256` signature algorithms to
verify the signature of the JWT from the JWT issuer.

`pkc_jwkset_path`::
The file name or URL to a JSON Web Key Set (JWKS) with the public key material that
the JWT Realm uses for verifying token signatures. A value is considered a file name
if it does not begin with `https`. The file name
is resolved relative to the {es} configuration directory. If a URL is provided, then
it must begin with `https://` (`http://` is not supported).
{es} automatically caches the JWK set and will attempt to refresh the
JWK set upon signature verification failure, as this might indicate that the JWT Provider has
rotated the signing keys.

`claims.principal`::
The name of the JWT claim that contains the user's principal (username).

The following is an example snippet for configure a JWT realm for handling
access tokens:

[source,yaml]
----
xpack.security.authc.realms.jwt.jwt2:
  order: 4
  token_type: access_token
  client_authentication.type: shared_secret
  allowed_issuer: "https://issuer.example.com/jwt/"
  allowed_subjects: [ "123456-compute@admin.example.com" ]
  allowed_subject_patterns: [ "wild*@developer?.example.com", "/[a-z]+<1-10>\\@dev\\.example\\.com/"]
  allowed_audiences: [ "elasticsearch" ]
  required_claims:
    token_use: access
    version: ["1.0", "2.0"]
  allowed_signature_algorithms: [RS256,HS256]
  pkc_jwkset_path: "https://idp-42.example.com/.well-known/configuration"
  fallback_claims.sub: client_id
  fallback_claims.aud: scope
  claims.principal: sub
----

`token_type`::
Instructs the realm to treat and validate incoming JWTs as access tokens (`access_token`).

`allowed_subjects`::
Specifies a list of JWT subjects that the realm will allow.
These values are typically URLs, UUIDs, or other case-sensitive string values.

`allowed_subject_patterns`::
Analogous to `allowed_subjects` but it accepts a list of <<regexp-syntax,Lucene regexp>>
and wildcards for the allowed JWT subjects. Wildcards use the `*` and `?` special
characters (which are escaped by `\`) to mean "any string" and "any single character"
respectively, for example "a?\\**", matches "a1*" and "ab*whatever", but not "a", "abc", or "abc*"
(in Java strings `\` must itself be escaped by another `\`).
<<regexp-syntax,Lucene regexp>> must be enclosed between `/`,
for example "/https?://[^/]+/?/" matches any http or https URL with no path component
(matches "https://elastic.co/" but not "https://elastic.co/guide").

NOTE: At least one of the `allowed_subjects` or `allowed_subject_patterns` settings must be specified
(and be non-empty) when `token_type` is `access_token`.

NOTE: When both `allowed_subjects` and `allowed_subject_patterns` settings are specified
an incoming JWT's `sub` claim is accepted if it matches any of the two lists.

`required_claims`::
Specifies a list of key/value pairs for additional verifications to be performed
against a JWT. The values are either a string or an array of strings.

`fallback_claims.sub`::
The name of the JWT claim to extract the subject information if the `sub` claim does not exist.
This setting is only available when `token_type` is `access_token`.
The fallback is applied everywhere the `sub` claim is used.
In the above snippet, it means the `claims.principal` will also fallback to `client_id`
if `sub` does not exist.

`fallback_claims.aud`::
The name of the JWT claim to extract the audiences information if the `aud` claim does not exist.
This setting is only available when `token_type` is `access_token`.
The fallback is applied everywhere the `aud` claim is used.

--

. After defining settings, use the
{ref}/elasticsearch-keystore.html[`elasticsearch-keystore`] tool to store
values for secure settings in the {es} keystore.

.. Store the `shared_secret` value for `client_authentication.type`:
+
[source,shell]
----
bin/elasticsearch-keystore add xpack.security.authc.realms.jwt.jwt1.client_authentication.shared_secret
----

.. Store the HMAC keys for `allowed_signature_algorithms`, which use the HMAC
SHA-256 algorithm `HS256` in the example:
+
[source,shell]
----
bin/elasticsearch-keystore add-file xpack.security.authc.realms.jwt.jwt1.hmac_jwkset <path> <1>
----
<1> Path to a JWKS, which is a resource for a set of JSON-encoded secret keys.
The file can be removed after you load the contents into the {es} keystore.
+
[NOTE]
====
Using the JWKS is preferred. However, you can add an HMAC key in string format
using the following command. This format is compatible with HMAC UTF-8 keys, but
only supports a single key with no attributes. You can only use one HMAC format
(either `hmac_jwkset` or `hmac_key`) simultaneously.

[source,shell]
----
bin/elasticsearch-keystore add xpack.security.authc.realms.jwt.jwt1.hmac_key
----
====

[[jwt-validation]]
==== JWT encoding and validation
JWTs can be parsed into three pieces:

Header::
Provides information about how to validate the token.

Claims::
Contains data about the calling user or application.

Signature::
The data that's used to validate the token.

[source,js]
----
Header: {"typ":"JWT","alg":"HS256"}
Claims: {"aud":"aud8","sub":"security_test_user","iss":"iss8","exp":4070908800,"iat":946684800}
Signature: UnnFmsoFKfNmKMsVoDQmKI_3-j95PCaKdgqqau3jPMY
----
// NOTCONSOLE

This example illustrates a partial decoding of a JWT. The validity period is
from 2000 to 2099 (inclusive), as defined by the issue time (`iat`) and
expiration time (`exp`). JWTs typically have a validity period shorter than
100 years, such as 1-2 hours or 1-7 days, not an entire human life.

The signature in this example is deterministic because the header, claims, and
HMAC key are fixed. JWTs typically have a `nonce` claim to make the signature
non-deterministic. The supported JWT encoding is JSON Web Signature (JWS), and
the JWS `Header` and `Signature` are validated using OpenID Connect ID Token
validation rules. Some validation is customizable through
<<ref-jwt-settings,JWT realm settings>>.

[[jwt-validation-header]]
===== Header claims
The header claims indicate the token type and the algorithm used to sign the
token.

`alg`::
(Required, String) Indicates the algorithm that was used to sign the token, such
as `HS256`. The algorithm must be in the realm's allow list.

`typ`::
(Optional, String) Indicates the token type.
+
For an ID token, this must be
+
 - `JWT`

+
For access tokens, this must be one of
+
 - `JWT`
 - `at+jwt`

[[jwt-validation-payload]]
===== Payload claims
Tokens contain several claims, which provide information about the user
who is issuing the token, and the token itself.
Depending on the token type, these information can optionally be identified
by different claims.

====== JWT payload claims
The following claims are validated by a subset of OIDC ID token rules.

{es} doesn't validate `nonce` claims, but a custom JWT issuer can add a
random `nonce` claim to introduce entropy into the signature.

NOTE: You can relax validation of any of the time-based claims by setting
`allowed_clock_skew`. This value sets the maximum allowed clock skew before
validating JWTs with respect to their authentication time (`auth_time`),
creation (`iat`), not before (`nbf`), and expiration times (`exp`).

`iss`::
(Required, String) Denotes the issuer that created the ID token. The value must
be an exact, case-sensitive match to the value in the `allowed_issuer` setting.

`sub`::
(Required*, String) Indicates the subject that the ID token is created for.
If the JWT realm is of the `id_token` type, this claim is mandatory.
A JWT realm of the `id_token` type by defaults accepts all subjects.
A JWT realm of the access_token type must specify the `allowed_subjects` setting and the subject value
must be an exact, case-sensitive match to any of the CSV values in the
allowed_subjects setting.
A JWT realm of the access_token type can specify a fallback claim that will
be used in place where the `sub` claim does not exist.

`aud`::
(Required*, String) Indicates the audiences that the ID token is for, expressed as a
comma-separated value (CSV). One of the values must be an exact, case-sensitive
match to any of the CSV values in the `allowed_audiences` setting.
If the JWT realm is of the `id_token` type, this claim is mandatory.
A JWT realm of the `access_token` type can specify a fallback claim that will
be used in place where the `aud` claim does not exist.

`exp`::
(Required, integer) Expiration time for the ID token, expressed in UTC
seconds since epoch.

`iat`::
(Required, integer) Time that the ID token was issued, expressed in UTC
seconds since epoch.

`nbf`::
(Optional, integer) Indicates the time before which the JWT must not be accepted,
expressed as UTC seconds since epoch.
This claim is optional. If it exists, a JWT realm of `id_token` type will verify
it, while a JWT realm of `access_token` will just ignore it.

`auth_time`::
(Optional, integer) Time when the user authenticated to the JWT issuer,
expressed as UTC seconds since epoch.
This claim is optional. If it exists, a JWT realm of `id_token` type will verify
it, while a JWT realm of `access_token` will just ignore it.


[[jwt-validation-payload-es]]
====== {es} settings for consuming JWT claims
{es} uses JWT claims for the following settings.

`principal`::
(Required, String) Contains the user's principal (username). The value is
configurable using the realm setting `claims.principal`.
You can configure an optional regular expression using the
`claim_patterns.principal` to extract a substring.

`groups`::
(Optional, JSON array) Contains the user's group membership.
The value is configurable using the realm setting `claims.groups`. You can
configure an optional regular expression using the realm setting
`claim_patterns.groups` to extract a substring value.

`name`::
(Optional, String) Contains a human-readable identifier that identifies the
subject of the token. The value is configurable using the realm setting
`claims.name`. You can configure an optional regular expression using the realm
setting `claim_patterns.name` to extract a substring value.

`mail`::
(Optional, String) Contains the e-mail address to associate with the user. The
value is configurable using the realm setting `claims.mail`. You can configure an
optional regular expression using the realm setting `claim_patterns.mail` to
extract a substring value.

`dn`::
(Optional, String) Contains the user's Distinguished Name (DN), which uniquely
identifies a user or group. The value is configurable using the realm setting
`claims.dn`. You can configure an optional regular expression using the realm
setting `claim_patterns.dn` to extract a substring value.

[[jwt-authorization]]
==== JWT realm authorization
The JWT realm supports authorization with the create or update role mappings API,
or delegating authorization to another realm. You cannot use these methods
simultaneously, so choose whichever works best for your environment.

IMPORTANT: You cannot map roles in the JWT realm using the `role_mapping.yml`
file.

[[jwt-authorization-role-mapping]]
===== Authorizing with the role mapping API
You can use the
<<security-api-put-role-mapping,create or update role mappings API>> to define
role mappings that determine which roles should be assigned to each user based on
their username, groups, or other metadata.

[source,console]
----
PUT /_security/role_mapping/jwt1_users?refresh=true
{
  "roles" : [ "user" ],
  "rules" : { "all" : [
      { "field": { "realm.name": "jwt1" } },
      { "field": { "username": "principalname1" } },
      { "field": { "dn": "CN=Principal Name 1,DC=example.com" } },
      { "field": { "groups": "group1" } },
      { "field": { "metadata.jwt_claim_other": "other1" } }
  ] },
  "enabled": true
}
----

If you use this API in the JWT realm, the following claims are available for
role mapping:

`principal`::
(Required, String) Principal claim that is used as the {es} user's username.

`dn`::
(Optional, String) Distinguished Name (DN) that is used as the {es} user's DN.

`groups`::
(Optional, String) Comma-separated value (CSV) list that is used as the {es}
user's list of groups.

`metadata`::
(Optional, object) Additional metadata about the user, such as strings, integers,
boolean values, and collections that are used as the {es} user's metadata.
These values are key value pairs formatted as
`metadata.jwt_claim_<key>` = `<value>`.

[[jwt-authorization-delegation]]
===== Delegating JWT authorization to another realm
If you <<authorization_realms,delegate authorization>> to other realms from the
JWT realm, only the `principal` claim is available for role lookup. When
delegating the assignment and lookup of roles to another realm from the JWT
realm, claims for `dn`, `groups`, `mail`, `metadata`, and `name` are not used
for the {es} user's values. Only the JWT `principal` claim is passed to the
delegated authorization realms. The realms that are delegated for authorization
- not the JWT realm - become responsible for populating all of the {es} user's
values.

The following example shows how you define delegation authorization in the
`elasticsearch.yml` file to multiple other realms from the JWT realm. A JWT
realm named `jwt2` is delegating authorization to multiple realms:

[source,yaml]
----
xpack.security.authc.realms.jwt.jwt2.authorization_realms: file1,native1,ldap1,ad1
----

You can then use the
<<security-api-put-role-mapping,create or update role mappings API>> to map
roles to the authorizing realm. The following example maps roles in the `native1`
realm for the `principalname1` JWT principal.

[source,console]
----
PUT /_security/role_mapping/native1_users?refresh=true
{
  "roles" : [ "user" ],
  "rules" : { "all" : [
      { "field": { "realm.name": "native1" } },
      { "field": { "username": "principalname1" } }
  ] },
  "enabled": true
}
----

If realm `jwt2` successfully authenticates a client with a JWT for principal
`principalname1`, and delegates authorization to one of the listed realms
(such as `native1`), then that realm can look up the {es} user's values. With
this defined role mapping, the realm can also look up this role mapping rule
linked to realm `native1`.

[[jwt-realm-runas]]
===== Applying the `run_as` privilege to JWT realm users
{es} can retrieve roles for a JWT user through either role mapping or
delegated authorization. Regardless of which option you choose, you can apply the
<<run-as-privilege-apply,`run_as` privilege>> to a role so that a user can
submit authenticated requests to "run as" a different user. To submit requests as
another user, include the `es-security-runas-user` header in your requests.
Requests run as if they were issued from that user and {es} uses their roles.

For example, let's assume that there's a user with the username `user123_runas`.
The following request creates a user role named `jwt_role1`, which specifies a
`run_as` user with the `user123_runas` username. Any user with the `jwt_role1`
role can issue requests as the specified `run_as` user.

[source,console]
----
POST /_security/role/jwt_role1?refresh=true
{
  "cluster": ["manage"],
  "indices": [ { "names": [ "*" ], "privileges": ["read"] } ],
  "run_as": [ "user123_runas" ],
  "metadata" : { "version" : 1 }
}
----

You can then map that role to a user in a specific realm. The following request
maps the `jwt_role1` role to a user with the username `user2` in the `jwt2` JWT
realm. This means that {es} will use the `jwt2` realm to authenticate the user
named `user2`. Because `user2` has a role (the `jwt_role1` role) that includes
the `run_as` privilege, {es} retrieves the role mappings for the `user123_runas`
user and uses the roles for that user to submit requests.

[source,console]
----
POST /_security/role_mapping/jwt_user1?refresh=true
{
  "roles": [ "jwt_role1"],
  "rules" : { "all" : [
      { "field": { "realm.name": "jwt2" } },
      { "field": { "username": "user2" } }
  ] },
  "enabled": true,
  "metadata" : { "version" : 1 }
}
----

After mapping the roles, you can make an
<<security-api-authenticate,authenticated call>> to {es} using a JWT and include
the `ES-Client-Authentication` header:

[[jwt-auth-shared-secret-scheme-example]]
[source,sh]
----
curl -s -X GET -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJhdWQiOlsiZXMwMSIsImVzMDIiLCJlczAzIl0sInN1YiI6InVzZXIyIiwiaXNzIjoibXktaXNzdWVyIiwiZXhwIjo0MDcwOTA4ODAwLCJpYXQiOjk0NjY4NDgwMCwiZW1haWwiOiJ1c2VyMkBzb21ldGhpbmcuZXhhbXBsZS5jb20ifQ.UgO_9w--EoRyUKcWM5xh9SimTfMzl1aVu6ZBsRWhxQA" -H "ES-Client-Authentication: sharedsecret test-secret" https://localhost:9200/_security/_authenticate
----
// NOTCONSOLE

The response includes the user who submitted the request (`user2`), including
the `jwt_role1` role that you mapped to this user in the JWT realm:

[source,sh]
----
{"username":"user2","roles":["jwt_role1"],"full_name":null,"email":"user2@something.example.com",
"metadata":{"jwt_claim_email":"user2@something.example.com","jwt_claim_aud":["es01","es02","es03"],
"jwt_claim_sub":"user2","jwt_claim_iss":"my-issuer"},"enabled":true,"authentication_realm":
{"name":"jwt2","type":"jwt"},"lookup_realm":{"name":"jwt2","type":"jwt"},"authentication_type":"realm"}
%
----

If you want to specify a request as the `run_as` user, include the
`es-security-runas-user` header with the name of the user that you want to
submit requests as. The following request uses the `user123_runas` user:

[source,sh]
----
curl -s -X GET -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJhdWQiOlsiZXMwMSIsImVzMDIiLCJlczAzIl0sInN1YiI6InVzZXIyIiwiaXNzIjoibXktaXNzdWVyIiwiZXhwIjo0MDcwOTA4ODAwLCJpYXQiOjk0NjY4NDgwMCwiZW1haWwiOiJ1c2VyMkBzb21ldGhpbmcuZXhhbXBsZS5jb20ifQ.UgO_9w--EoRyUKcWM5xh9SimTfMzl1aVu6ZBsRWhxQA" -H "ES-Client-Authentication: sharedsecret test-secret" -H "es-security-runas-user: user123_runas" https://localhost:9200/_security/_authenticate
----
// NOTCONSOLE

In the response, you'll see that the `user123_runas` user submitted the request,
and {es} used the `jwt_role1` role:

[source,sh]
----
{"username":"user123_runas","roles":["jwt_role1"],"full_name":null,"email":null,"metadata":{},
"enabled":true,"authentication_realm":{"name":"jwt2","type":"jwt"},"lookup_realm":{"name":"native",
"type":"native"},"authentication_type":"realm"}%
----

[[jwt-realm-jwkset-reloading]]
===== PKC JWKS reloading
JWT authentication supports signature verification using PKC (Public Key Cryptography)
or HMAC algorithms.

PKC JSON Web Token Key Sets (JWKS) can contain public RSA and EC keys. HMAC JWKS
or an HMAC UTF-8 JWK contain secret keys. JWT issuers typically rotate PKC JWKS
more frequently (such as daily), because RSA and EC public keys are designed to
be easier to distribute than secret keys like HMAC.

JWT realms load a PKC JWKS and an HMAC JWKS or HMAC UTF-8 JWK at startup. JWT
realms can also reload PKC JWKS contents at runtime; a reload is triggered by
signature validation failures.

NOTE: HMAC JWKS or HMAC UTF-8 JWK reloading is not supported at this time.

Load failures, parse errors, and configuration errors prevent a node from
starting (and restarting). However, runtime PKC reload errors and recoveries are
handled gracefully.

All other JWT realm validations are checked before a signature failure can
trigger a PKC JWKS reload. If multiple JWT authentication signature failures
occur simultaneously with a single {es} node, reloads are combined to reduce
the reloads that are sent externally.

Separate reload requests cannot be combined if JWT signature failures trigger:

* PKC JWKS reloads in different {es} nodes
* PKC JWKS reloads in the same {es} node at different times

[IMPORTANT]
====
Enabling client authentication (`client_authentication.type`) is strongly
recommended. Only trusted client applications and realm-specific JWT users can
trigger PKC reload attempts. Additionally, configuring the following
<<ref-jwt-settings,JWT security settings>> is recommended:

* `allowed_audiences`
* `allowed_clock_skew`
* `allowed_issuer`
* `allowed_signature_algorithms`
====

[[hmac-oidc-example]]
==== Authorizing to the JWT realm with an HMAC UTF-8 key
The following settings are for a JWT issuer, {es}, and a client of {es}. The
example HMAC key is in an OIDC format that's compatible with HMAC. The key bytes
are the UTF-8 encoding of the UNICODE characters.

IMPORTANT: HMAC UTF-8 keys need to be longer than HMAC random byte keys to
achieve the same key strength.

[[hmac-oidc-example-jwt-issuer]]
===== JWT issuer
The following values are for the bespoke JWT issuer.

[source,js]
----
Issuer:     iss8
Audiences:  aud8
Algorithms: HS256
HMAC UTF-8: hmac-oidc-key-string-for-hs256-algorithm
----
// NOTCONSOLE

[[hmac-oidc-example-jwt-realm]]
===== JWT realm settings
To define a JWT realm, add the following realm settings to `elasticsearch.yml`.

[source,yaml]
----
xpack.security.authc.realms.jwt.jwt8.order: 8 <1>
xpack.security.authc.realms.jwt.jwt8.allowed_issuer: iss8
xpack.security.authc.realms.jwt.jwt8.allowed_audiences: [aud8]
xpack.security.authc.realms.jwt.jwt8.allowed_signature_algorithms: [HS256]
xpack.security.authc.realms.jwt.jwt8.claims.principal: sub
xpack.security.authc.realms.jwt.jwt8.client_authentication.type: shared_secret
----
<1> In {ecloud}, the realm order starts at `2`. `0` and `1` are reserved in the
realm chain on {ecloud}.

===== JWT realm secure settings
After defining the realm settings, use the
{ref}/elasticsearch-keystore.html[`elasticsearch-keystore`] tool to add the
following secure settings to the {es} keystore. In {ecloud}, you define settings
for the {es} keystore under **Security** in your deployment.

[source,yaml]
----
xpack.security.authc.realms.jwt.jwt8.hmac_key: hmac-oidc-key-string-for-hs256-algorithm
xpack.security.authc.realms.jwt.jwt8.client_authentication.shared_secret: client-shared-secret-string
----

===== JWT realm role mapping rule
The following request creates role mappings for {es} in the `jwt8` realm for
the user `principalname1`:

[source,console]
----
PUT /_security/role_mapping/jwt8_users?refresh=true
{
  "roles" : [ "user" ],
  "rules" : { "all" : [
      { "field": { "realm.name": "jwt8" } },
      { "field": { "username": "principalname1" } }
  ] },
  "enabled": true
}
----

[[hmac-oidc-example-request-headers]]
===== Request headers
The following header settings are for an {es} client.

[source,js]
----
Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJpc3M4IiwiYXVkIjoiYXVkOCIsInN1YiI6InNlY3VyaXR5X3Rlc3RfdXNlciIsImV4cCI6NDA3MDkwODgwMCwiaWF0Ijo5NDY2ODQ4MDB9.UnnFmsoFKfNmKMsVoDQmKI_3-j95PCaKdgqqau3jPMY
ES-Client-Authentication: SharedSecret client-shared-secret-string
----
// NOTCONSOLE

You can use this header in a `curl` request to make an authenticated call to
{es}. Both the bearer token and the client authorization token must be
specified as separate headers with the `-H` option:

[source,sh]
----
curl -s -X GET -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJpc3M4IiwiYXVkIjoiYXVkOCIsInN1YiI6InNlY3VyaXR5X3Rlc3RfdXNlciIsImV4cCI6NDA3MDkwODgwMCwiaWF0Ijo5NDY2ODQ4MDB9.UnnFmsoFKfNmKMsVoDQmKI_3-j95PCaKdgqqau3jPMY" -H "ES-Client-Authentication: SharedSecret client-shared-secret-string" https://localhost:9200/_security/_authenticate
----
// NOTCONSOLE

If you used role mapping in the JWT realm, the response includes the user's
`username`, their `roles`, metadata about the user, and the details about the
JWT realm itself.

[source,sh]
----
{"username":"user2","roles":["jwt_role1"],"full_name":null,"email":"user2@something.example.com",
"metadata":{"jwt_claim_email":"user2@something.example.com","jwt_claim_aud":["es01","es02","es03"],
"jwt_claim_sub":"user2","jwt_claim_iss":"my-issuer"},"enabled":true,"authentication_realm":
{"name":"jwt2","type":"jwt"},"lookup_realm":{"name":"jwt2","type":"jwt"},"authentication_type":"realm"}
----
