Authentication identifies an individual. To gain access to restricted resources, a user must prove their identity, via passwords, credentials, or some other means (typically referred to as authentication tokens).
A realm is an authentication mechanism, which Shield uses to resolve and authenticate users and their roles. Shield currently provides four realm types:
A native authentication system built into Shield and available by default. See Configuring an esusers Realm.
Authentication via an external Lightweight Directory Protocol. See Configuring an LDAP Realm.
Authentication via an external Active Directory service. See Configuring an Active Directory Realm.
Authentication through the use of trusted X.509 certificates. See Configuring a PKI Realm.
esusers, LDAP, and Active Directory realms authenticate using the username and password authentication tokens.
Realms live within a realm chain. It is essentially a prioritized list of configured realms (typically of various types).
The order of the list determines the order in which the realms will be consulted. During the authentication process,
Shield will consult and try to authenticate the request one realm at a time. Once one of the realms successfully
authenticates the request, the authentication is considered to be successful and the authenticated user will be associated
with the request (which will then proceed to the authorization phase). If a realm cannot authenticate the request, the
next in line realm in the chain will be consulted. If all realms in the chain could not authenticate the request, the
authentication is then considered to be unsuccessful and an authentication error will be returned (as HTTP status code
Shield attempts to authenticate to each configured realm sequentially. Some systems (e.g. Active Directory) have a temporary lock-out period after several successive failed login attempts. If the same username exists in multiple realms, unintentional account lockouts are possible. For more information, please see here.
For example, if
UserA exists in both Active Directory and esusers, and the Active Directory realm is checked first and
esusers is checked second, an attempt to authenticate as
UserA in the esusers realm would first attempt to authenticate
against Active Directory and fail, before successfully authenticating against the esusers realm. Because authentication is
verified on each request, the Active Directory realm would be checked - and fail - on each request for
UserA in the esusers
realm. In this case, while the Shield request completed successfully, the account on Active Directory would have received
several failed login attempts, and that account may become temporarily locked out. Plan the order of your realms accordingly.
The realm chain can be configured in the
elasticsearch.yml file. When not explicitly configured, a default chain will be
created that only holds the
esusers realm in it. When explicitly configured, the created chain will be the exact reflection
of the configuration (e.g. the only realms in the chain will be those configured realms that are enabled)
The following snippet shows an example of realms configuration:
shield.authc: realms: esusers: type: esusers order: 0 ldap1: type: ldap order: 1 enabled: false url: 'url_to_ldap1' ... ldap2: type: ldap order: 2 url: 'url_to_ldap2' ... ad1: type: active_directory order: 3 url: 'url_to_ad'
As can be seen above, each realm has a unique name that identifies it. There are three settings that are common to all realms:
type(required) - Identifies the type of the ream (currently can be
active_directory). The realm type determines what other settings the realms should be configured with.
order(optional) - Defines the priority/index of the realm within the realm chain. This will determine when the realm will be consulted during authentication.
enabled(optional) - When set to
falsethe realm will be disabled and will not be added to the realm chain. This is useful for debugging purposes, where one can remove a realm from the chain without deleting and losing its configuration.
The realm types can roughly be categorized to two categories:
internal- Internal realm types are realms that are internal to Elasticsearch and don’t require any communication with external parties - they are fully managed by shield. There can only be a maximum of one configured realm per internal realm type. (Currently, only one internal realm type exists -
external- External realm types are realms that require interaction with parties/components external to Elasticsearch, typically, with enterprise level identity management systems. Unlike the
internalrealms, there can be as many
externalrealms as one would like - each with a unique name and different settings. (Currently the only
externalrealm types that exist are