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SAML

The Security plugin supports user authentication through SAML single sign-on. The Security plugin implements the web browser SSO profile of the SAML 2.0 protocol.

This profile is meant for use with web browsers. It is not a general-purpose way of authenticating users against the Security plugin, so its primary use case is to support OpenSearch Dashboards single sign-on.

Docker example

We provide a fully functional example that can help you understand how to use SAML with OpenSearch Dashboards.

1. Download and unzip the example zip file.
2. At the command line, run docker-compose up.

3. Review the files:

   • docker-compose.yml defines two OpenSearch nodes, an OpenSearch Dashboards server, and a SAML server.
   • custom-opensearch_dashboards.yml add a few SAML settings to the default opensearch_dashboards.yml file.
   • config.yml configures SAML for authentication.

4. Access OpenSearch Dashboards at http://localhost:5601. Note that OpenSearch Dashboards immediately redirects you to the SAML login page.

5. Log in as admin with a password of admin.

6. After logging in, note that your user in the upper-right is SAMLAdmin, as defined in /var/www/simplesamlphp/config/authsources.php of the SAML server.

7. If you want to examine the SAML server, run docker ps to find its container ID and then docker exec -it <container-id> /bin/bash.

   In particular, you might find it helpful to review the contents of the /var/www/simplesamlphp/config/ and /var/www/simplesamlphp/metadata/ directories.

Activating SAML

To use SAML for authentication, you need to configure a respective authentication domain in the authc section of config/opensearch-security/config.yml. Because SAML works solely on the HTTP layer, you do not need any authentication_backend and can set it to noop. Place all SAML-specific configuration options in this chapter in the config section of the SAML HTTP authenticator:

authc:
  saml_auth_domain:
    http_enabled: true
    transport_enabled: false
    order: 1
    http_authenticator:
      type: saml
      challenge: true
      config:
        idp:
          metadata_file: okta.xml
          ...
    authentication_backend:
      type: noop

After you have configured SAML in config.yml, you must also activate it in OpenSearch Dashboards.

Running multiple authentication domains

We recommend adding at least one other authentication domain, such as LDAP or the internal user database, to support API access to OpenSearch without SAML. For OpenSearch Dashboards and the internal OpenSearch Dashboards server user, you also must add another authentication domain that supports basic authentication. This authentication domain should be placed first in the chain, and the challenge flag must be set to false:

authc:
  basic_internal_auth_domain:
    http_enabled: true
    transport_enabled: true
    order: 0
    http_authenticator:
      type: basic
      challenge: false
    authentication_backend:
      type: internal
  saml_auth_domain:
    http_enabled: true
    transport_enabled: false
    order: 1
    http_authenticator:
      type: saml
      challenge: true
      config:
        ...
    authentication_backend:
      type: noop

Identity provider metadata

A SAML identity provider (IdP) provides a SAML 2.0 metadata file describing the IdP’s capabilities and configuration. The Security plugin can read IdP metadata either from a URL or a file. The choice that you make depends on your IdP and your preferences. The SAML 2.0 metadata file is required.

IdP and service provider entity ID

An entity ID is a globally unique name for a SAML entity, either an IdP or a service provider (SP). The IdP entity ID is usually provided by your IdP. The SP entity ID is the name of the configured application or client in your IdP. We recommend adding a new application for OpenSearch Dashboards and using the URL of your OpenSearch Dashboards installation as the SP entity ID.

Time disparity compensation for JWT validation

Occasionally you may find that the clock times between the authentication server and the OpenSearch node are not perfectly synchronized. When this is the case, even by a few seconds, the system that either issues or receives a JSON Web Token (JWT) may try to validate nbf (not before) and exp (expiration) claims and fail to authenticate the user due to the time disparity.

By default, OpenSearch Security allows for a window of 30 seconds to compensate for possible misalignment between server clock times. To set a custom value for this feature and override the default, you can add the jwt_clock_skew_tolerance_seconds setting to the config.yml.

http_authenticator:
  type: saml
  challenge: true
  config:
    idp:
      metadata_file: okta.xml
    jwt_clock_skew_tolerance_seconds: 20

OpenSearch Dashboards settings

The web browser SSO profile exchanges information through HTTP GET or POST. For example, after you log in to your IdP, it sends an HTTP POST back to OpenSearch Dashboards containing the SAML response. You must configure the base URL of your OpenSearch Dashboards installation where the HTTP requests are being sent to.

Username and Role attributes

Subjects (for example, user names) are usually stored in the NameID element of a SAML response:

<saml2:Subject>
  <saml2:NameID>admin</saml2:NameID>
  ...
</saml2:Subject>

If your IdP is compliant with the SAML 2.0 specification, you do not need to set anything special. If your IdP uses a different element name, you can also specify its name explicitly.

Role attributes are optional. However, most IdPs can be configured to add roles in the SAML assertions as well. If present, you can use these roles in your role mappings:

<saml2:Attribute Name='Role'>
  <saml2:AttributeValue >Everyone</saml2:AttributeValue>
  <saml2:AttributeValue >Admins</saml2:AttributeValue>
</saml2:Attribute>

If you want to extract roles from the SAML response, you need to specify the element name that contains the roles.

Request signing

Requests from the Security plugin to the IdP can optionally be signed. Use the following settings to configure request signing.

The private key must be in PKCS#8 format. If you want to use an encrypted key, it must be encrypted with a PKCS#12-compatible algorithm (3DES).

The Security plugin supports the following signature algorithms.

Logout

Usually, IdPs provide information about their individual logout URL in their SAML 2.0 metadata. If this is the case, the Security plugin uses them to render the correct logout link in OpenSearch Dashboards. If your IdP does not support an explicit logout, you can force a re-login when the user visits OpenSearch Dashboards again.

Currently, the Security plugin supports only the HTTP-Redirect logout binding. Make sure this is configured correctly in your IdP.

Exchange key settings

SAML, unlike other protocols, is not meant to be used for exchanging user credentials with each request. The Security plugin trades the SAML response for a lightweight JWT that stores the validated user attributes. This token is signed by an exchange key of your choice. Note that when you change this key, all tokens signed with it become invalid immediately.

TLS settings

If you are loading the IdP metadata from a URL, we recommend that you use SSL/TLS. If you use an external IdP like Okta or Auth0 that uses a trusted certificate, you usually do not need to configure anything. If you host the IdP yourself and use your own root CA, you can customize the TLS settings as follows. These settings are used only for loading SAML metadata over HTTPS.

Example:

authc:
  saml_auth_domain:
    http_enabled: true
    transport_enabled: false
    order: 1
    http_authenticator:
      type: saml
      challenge: true
      config:
        idp:
          enable_ssl: true
          verify_hostnames: true
          ...
    authentication_backend:
      type: noop

Certificate validation

Configure the root CA used for validating the IdP TLS certificate by setting one of the following configuration options:

config:
  idp:
    pemtrustedcas_filepath: path/to/trusted_cas.pem

config:
  idp:
    pemtrustedcas_content: |-
      MIID/jCCAuagAwIBAgIBATANBgkqhkiG9w0BAQUFADCBjzETMBEGCgmSJomT8ixk
      ARkWA2NvbTEXMBUGCgmSJomT8ixkARkWB2V4YW1wbGUxGTAXBgNVBAoMEEV4YW1w
      bGUgQ29tIEluYy4xITAfBgNVBAsMGEV4YW1wbGUgQ29tIEluYy4gUm9vdCBDQTEh
      ...

Client authentication

The Security plugin can use TLS client authentication when fetching the IdP metadata. If enabled, the Security plugin sends a TLS client certificate to the IdP for each metadata request. Use the following keys to configure client authentication.

Enabled ciphers and protocols

You can limit the allowed ciphers and TLS protocols for the IdP connection. For example, you can only enable strong ciphers and limit the TLS versions to the most recent ones.

Minimal configuration example

The following example shows the minimal configuration:

authc:
  saml_auth_domain:
    http_enabled: true
    transport_enabled: false
    order: 1
    http_authenticator:
      type: saml
      challenge: true
      config:
        idp:
          metadata_file: metadata.xml
          entity_id: http://idp.example.com/
        sp:
          entity_id: https://opensearch-dashboards.example.com
        kibana_url: https://opensearch-dashboards.example.com:5601/
        roles_key: Role
        exchange_key: 'peuvgOLrjzuhXf ...'
    authentication_backend:
      type: noop

OpenSearch Dashboards configuration

Because most of the SAML-specific configuration is done in the Security plugin, just activate SAML in your opensearch_dashboards.yml by adding the following:

opensearch_security.auth.type: "saml"

In addition, you must add the OpenSearch Dashboards endpoint for validating the SAML assertions to your allow list:

server.xsrf.allowlist: ["/_opendistro/_security/saml/acs"]

If you use the logout POST binding, you also need to ad the logout endpoint to your allow list:

server.xsrf.allowlist: ["/_opendistro/_security/saml/acs", "/_opendistro/_security/saml/logout"]

To include SAML with other authentication types in the Dashboards sign-in window, see Configuring sign-in options.

Session management with additional cookies

To improve session management—especially for users who have multiple roles assigned to them—Dashboards provides an option to split cookie payloads into multiple cookies and then recombine the payloads when receiving them. This can help prevent larger SAML assertions from exceeding size limits for each cookie. The two settings in the following example allow you to set a prefix name for additional cookies and specify the number of them. They are added to the opensearch_dashboards.yml file. The default number of additional cookies is three:

opensearch_security.saml.extra_storage.cookie_prefix: security_authentication_saml
opensearch_security.saml.extra_storage.additional_cookies: 3

Note that reducing the number of additional cookies can cause some of the cookies that were in use before the change to stop working. We recommend establishing a fixed number of additional cookies and not changing the configuration after that.

If the ID token from the IdP is especially large, OpenSearch may throw a server log authentication error indicating that the HTTP header is too large. In this case, you can increase the value for the http.max_header_size setting in the opensearch.yml file.

IdP-initiated SSO

To use IdP-initiated SSO, set the Assertion Consumer Service endpoint of your IdP to this:

/_opendistro/_security/saml/acs/idpinitiated

Then add this endpoint to server.xsrf.allowlist in opensearch_dashboards.yml:

server.xsrf.allowlist: ["/_opendistro/_security/saml/acs/idpinitiated", "/_opendistro/_security/saml/acs", "/_opendistro/_security/saml/logout"]