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Kerberos

Kerberos is a robust and secure method for user authentication that prevents passwords from being sent over the internet by issuing “tickets” for secure identity verification.

In order to use Kerberos authentication, you must set the following settings in opensearch.yml and config.yml.

OpenSearch node configuration

In opensearch.yml, define the following settings:

plugins.security.kerberos.krb5_filepath: '/etc/krb5.conf'
plugins.security.kerberos.acceptor_keytab_filepath: 'opensearch_keytab.tab'
plugins.security.kerberos.acceptor_principal: 'HTTP/localhost'

Due to security restrictions, the keytab file must be placed in config or a subdirectory, and the path in opensearch.yml must be relative, not absolute.

Cluster security configuration

The following example shows a typical Kerberos authentication domain in config.yml:

kerberos_auth_domain:
  enabled: true
  order: 1
  http_authenticator:
    type: kerberos
    challenge: true
    config:
      krb_debug: false
      strip_realm_from_principal: true
  authentication_backend:
    type: noop

Authentication through Kerberos when using a browser on an HTTP level is achieved using SPNEGO. Kerberos/SPNEGO implementations vary, depending on your browser and operating system. This is important when deciding if you need to set the challenge flag to true or false.

As with HTTP Basic Authentication, this flag determines how the Security plugin should react when no Authorization header is found in the HTTP request or if this header does not equal negotiate.

If set to true, the Security plugin sends a response with status code 401 and a WWW-Authenticate header set to negotiate. This tells the client (browser) to resend the request with the Authorization header set. If set to false, the Security plugin cannot extract the credentials from the request, and authentication fails. Setting challenge to false thus makes sense only if the Kerberos credentials are sent in the initial request.

Because Kerberos/SPNEGO authenticates users on an HTTP level, no additional authentication_backend is needed. Set this value to noop.