[role="xpack"]
[[setting-up-authentication]]
== User authentication

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).

The {stack} authenticates users by identifying the users behind the requests
that hit the cluster and verifying that they are who they claim to be. The
authentication process is handled by one or more authentication services called
<<realms,_realms_>>. 

You can use the native support for managing and authenticating users, or
integrate with external user management systems such as LDAP and Active
Directory. 

The {stack-security-features} provide built-in realms such as `native`,`ldap`,
`active_directory`, `pki`, `file`, `saml`, and `oidc`. If none of the built-in
realms meet your needs, you can also build your own custom realm and plug it
into the {stack}. 

When {security-features} are enabled, depending on the realms you've configured,
you must attach your user credentials to the requests sent to {es}. For example,
when using realms that support usernames and passwords you can simply attach 
{wikipedia}/Basic_access_authentication[basic auth] header to the requests.

The {security-features} provide two services: the token service and the api key
service. You can use these services to exchange the current authentication for
a token or key. This token or key can then be used as credentials for
authenticating new requests. These services are enabled by default when TLS/SSL
is enabled for HTTP.
