Backend configuration

The main configuration file for authentication and authorization backends is . It defines how the security plugin retrieves the user credentials, how it verifies these credentials, and how to fetch additional roles from backend systems (optional).

config.yml has three main parts:

For a more complete example, see the sample file on GitHub.

The http section has the following format:

anonymous_auth_enabled: <true|false>
xff: # optional section
  enabled: <true|false>
  internalProxies: <string> # Regex pattern
  remoteIpHeader: <string> # Name of the header in which to look. Typically: x-forwarded-for
  proxiesHeader: <string>
  trustedProxies: <string> # Regex pattern

If you disable anonymous authentication, the security plugin won’t initialize if you have not provided at least one authc.

Authentication

The authc section has the following format:

<name>:
  http_enabled: <true|false>
  transport_enabled: <true|false>
  order: <integer>
  http_authenticator:
    ...
  authentication_backend:
    ...

An entry in the authc section is called an authentication domain. It specifies where to get the user credentials and against which backend they should be authenticated.

You can use more than one authentication domain. Each authentication domain has a name (for example, basic_auth_internal), enabled flags, and an order. The order makes it possible to chain authentication domains together. The security plugin uses them in the order that you provide. If the user successfully authenticates with one domain, the security plugin skips the remaining domains.

http_authenticator specifies which authentication method that you want to use on the HTTP layer.

This is the syntax for defining an authenticator on the HTTP layer:

http_authenticator:
  type: <type>
  challenge: <true|false>
  config:
    ...

These are the allowed values for type:

• basic: HTTP basic authentication. No additional configuration is needed.
• kerberos: Kerberos authentication. Additional, Kerberos-specific configuration is needed.
• jwt: JSON web token authentication. Additional, is needed.
• clientcert: Authentication through a client TLS certificate. This certificate must be trusted by one of the root CAs in the truststore of your nodes.

After setting an HTTP authenticator, you must specify against which backend system you want to authenticate the user:

  type: <type>
  config:
    ...

These are the possible values for type:

• noop: No further authentication against any backend system is performed. Use noop if the HTTP authenticator has already authenticated the user completely, as in the case of JWT, Kerberos, or client certificate authentication.
• internal: Use the users and roles defined in internal_users.yml for authentication.
• ldap: Authenticate users against an LDAP server. This setting requires additional, LDAP-specific configuration settings.

After the user has been authenticated, the security plugin can optionally collect additional roles from backend systems. The authorization configuration has the following format:

authz:
  <name>:
    http_enabled: <true|false>
    transport_enabled: <true|false>
    authorization_backend:
      type: <type>
      config:
        ...

You can define multiple entries in this section the same way as you can for authentication entries. In this case, execution order is not relevant, so there is no order field.

These are the possible values for type:

• noop: Skip this step altogether.
• ldap: Fetch additional roles from an LDAP server. This setting requires .

Examples

The default config/opensearch-security/config.yml that ships with OpenSearch contains many configuration examples. Use these examples as a starting point, and customize them to your needs.

To set up HTTP basic authentication, you must enable it in the http_authenticator section of the configuration:

In most cases, you set the challenge flag to . The flag defines the behavior of the security plugin if the Authorization field in the HTTP header is not set.

If challenge is set to true, the security plugin sends a response with status UNAUTHORIZED (401) back to the client. If the client is accessing the cluster with a browser, this triggers the authentication dialog box, and the user is prompted to enter a user name and password.

Kerberos

Kerberos authentication does not work with OpenSearch Dashboards. To track OpenSearch’s progress in adding support for Kerberos in OpenSearch Dashboards, see issue #907 Kerberos Auth does not exist in the Dashboard’s Security Plugin repository. {: .warning }

Due to the nature of Kerberos, you must define some settings in opensearch.yml and some in config.yml.

In opensearch.yml, define the following:

plugins.security.kerberos.krb5_filepath: '/etc/krb5.conf'
plugins.security.kerberos.acceptor_keytab_filepath: 'eskeytab.tab'

plugins.security.kerberos.krb5_filepath defines the path to your Kerberos configuration file. This file contains various settings regarding your Kerberos installation, for example, the realm names, hostnames, and ports of the Kerberos key distribution center (KDC).

plugins.security.kerberos.acceptor_keytab_filepath defines the path to the keytab file, which contains the principal that the security plugin uses to issue requests against Kerberos.

plugins.security.kerberos.acceptor_principal: 'HTTP/localhost' defines the principal that the security plugin uses to issue requests against Kerberos. This value must be present in the keytab file.

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.

A typical Kerberos authentication domain in config.yml looks like this:

    authc:
      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 against Kerberos through 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 , 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.

As the name implies, setting krb_debug to true will output Kerberos-specific debugging messages to stdout. Use this setting if you encounter problems with your Kerberos integration.

If you set strip_realm_from_principal to true, the security plugin strips the realm from the user name.

Authentication backend

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

JSON web tokens (JWTs) are JSON-based access tokens that assert one or more claims. They are commonly used to implement single sign-on (SSO) solutions and fall in the category of token-based authentication systems:

1. A user logs in to an authentication server by providing credentials (for example, a user name and password).
2. The authentication server validates the credentials.
3. The authentication server creates an access token and signs it.
4. The authentication server returns the token to the user.
5. The user stores the access token.
6. The user sends the access token alongside every request to the service that it wants to use.
7. The service verifies the token and grants or denies access.

A JSON web token is self-contained in the sense that it carries all necessary information to verify a user within itself. The tokens are base64-encoded, signed JSON objects.

JSON web tokens consist of three parts:

1. Header
2. Payload
3. Signature

Header

The header contains information about the used signing mechanism, as shown in the following example:

{
  "alg": "HS256",
  "typ": "JWT"

In this case, the header states that the message was signed using HMAC-SHA256.

Payload

The payload of a JSON web token contains the so-called . A claim can be any piece of information about the user that the application that created the token has verified.

Public claims, on the other hand, can be created freely by the token issuer. They can contain arbitrary information, such as the user name and the roles of the user.

Example:

{
  "iss": "example.com",
  "exp": 1300819380,
  "name": "John Doe",
}

The issuer of the token calculates the signature of the token by applying a cryptographic hash function on the base64-encoded header and payload. These three parts are then concatenated using periods to form a complete JSON web token:

encoded = base64UrlEncode(header) + "." + base64UrlEncode(payload)
signature = HMACSHA256(encoded, 'secretkey');
jwt = encoded + "." + base64UrlEncode(signature)

Example:

Configure JSON web tokens

If JSON web tokens are the only authentication method that you use, disable the user cache by setting plugins.security.cache.ttl_minutes: 0.

Set up an authentication domain and choose jwt as the HTTP authentication type. Because the tokens already contain all required information to verify the request, challenge must be set to false and authentication_backend to noop.

Example:

jwt_auth_domain:
  enabled: true
  order: 0
  http_authenticator:
    type: jwt
    challenge: false
    config:
      signing_key: "base64 encoded key"
      jwt_header: "Authorization"
      jwt_url_parameter: null
      subject_key: null
      roles_key: null
  authentication_backend:
I    type: noop

The following table shows the configuration parameters.

Because JSON web tokens are self-contained and the user is authenticated on the HTTP level, no additional authentication_backend is needed. Set this value to noop.

Symmetric key algorithms: HMAC

Hash-based message authentication codes (HMACs) are a group of algorithms that provide a way of signing messages by means of a shared key. The key is shared between the authentication server and the security plugin. It must be configured as a base64-encoded value in the signing_key setting:

jwt_auth_domain:
  ...
    config:
      signing_key: "a3M5MjEwamRqOTAxOTJqZDE="
      ...

Asymmetric key algorithms: RSA and ECDSA

RSA and ECDSA are asymmetric encryption and digital signature algorithms and use a public/private key pair to sign and verify tokens. This means that they use a private key for signing the token, while the security plugin needs to know only the public key to verify it.

Because you cannot issue new tokens with the public key—and because you can make valid assumptions about the creator of the token—RSA and ECDSA are considered more secure than using HMAC.

To use RS256, you need to configure only the (non-base64-encoded) public RSA key as signing_key in the JWT configuration:

jwt_auth_domain:
  ...
    config:
      signing_key: |-
        -----BEGIN PUBLIC KEY-----
        MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQK...
        -----END PUBLIC KEY-----
      ...

The security plugin automatically detects the algorithm (RSA/ECDSA), and if necessary you can break the key into multiple lines.

The most common way of transmitting a JSON web token in an HTTP request is to add it as an HTTP header with the bearer authentication schema:

Authorization: Bearer <JWT>

The default name of the header is Authorization. If required by your authentication server or proxy, you can also use a different HTTP header name using the jwt_header configuration key.

As with HTTP basic authentication, you should use HTTPS instead of HTTP when transmitting JSON web tokens in HTTP requests.

URL parameters for HTTP requests

Although the most common way to transmit JWTs in HTTP requests is to use a header field, the security plugin also supports parameters. Configure the name of the GET parameter using the following key:

    config:
      signing_key: ...
      jwt_url_parameter: "parameter_name"
      subject_key: ...
      roles_key: ...

As with HTTP basic authentication, you should use HTTPS instead of HTTP.

Validated registered claims

The following registered claims are validated automatically:

• “iat” (Issued At) Claim
• “exp” (Expiration Time) Claim

Supported formats and algorithms