One of the first steps to using the Security plugin is to decide on an authentication backend, which handles [steps 2-3 of the authentication flow]({{site.url}}{{site.baseurl}}/security/authentication-backends/authc-index/#authentication-flow). The plugin has an internal user database, but many people prefer to use an existing authentication backend, such as an LDAP server, or some combination of the two.
The main configuration file for authentication and authorization backends is `config/opensearch-security/config.yml`. 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).
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.
-`jwt`: JSON Web Token (JWT) authentication. Additional configuration is needed. See [Configuring JWTs]({{site.url}}{{site.baseurl}}/security/authentication-backends/jwt/#configuring-jwts) for more information.
-`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:
-`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 or client certificate authentication.
-`ldap`: Authenticate users against an LDAP server. This setting requires [additional, LDAP-specific configuration settings]({{site.url}}{{site.baseurl}}/security/authentication-backends/ldap/).
After the user has been authenticated, the Security plugin can optionally collect additional roles from backend systems. The authorization configuration has the following format:
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.
-`ldap`: Fetch additional roles from an LDAP server. This setting requires [additional, LDAP-specific configuration settings]({{site.url}}{{site.baseurl}}/security/authentication-backends/ldap/).
In most cases, you set the `challenge` flag to `true`. 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.
If `challenge` is set to `false` and no `Authorization` header field is set, the Security plugin does not send a `WWW-Authenticate` response back to the client, and authentication fails. Consider using this setting if you have more than one challenge `http_authenticator` keys in your configured authentication domains. This might be the case, for example, when you plan to use basic authentication and OpenID Connect together.
## API rate limiting
API rate limiting is typically used to restrict the number of API calls that users can make in a set span of time, thereby helping to manage the rate of API traffic. For security purposes, rate limiting features have the potential to defend against DoS attacks, or repeated login attempts to gain access through trial and error, by restricting failed login attempts.
You have the option to configure the Security plugin for username rate limiting, IP address rate limiting, or both. These configurations are made in the `config.yml` file. See the following sections for information about each type of rate limiting configuration.
### Username rate limiting
This configuration limits login attempts by username. When a login fails, the username is blocked for any machine in the network. The following example shows `config.yml` file settings configured for username rate limiting:
```yml
auth_failure_listeners:
internal_authentication_backend_limiting:
type: username
authentication_backend: internal
allowed_tries: 3
time_window_seconds: 60
block_expiry_seconds: 60
max_blocked_clients: 100000
max_tracked_clients: 100000
```
{% include copy.html %}
The following table describes the individual settings for this type of configuration.
| Setting | Description |
| :--- | :--- |
| `type` | The type of rate limiting. In this case, `username`. |
| `authentication_backend` | The internal backend. Enter `internal`. |
| `allowed_tries` | The number of login attempts allowed before login is blocked. Be aware that increasing the number increases heap usage. |
| `time_window_seconds` | The window of time in which the value for `allowed_tries` is enforced. For example, if `allowed_tries` is `3` and `time_window_seconds` is `60`, a username has three attempts to log in successfully within a 60-second time span before login is blocked. |
| `block_expiry_seconds` | The duration of time that login remains blocked after a failed login. After this time elapses, login is reset and the username can attempt successful login again. |
| `max_blocked_clients` | The maximum number of blocked usernames. This limits heap usage to avoid a potential DoS. |
| `max_tracked_clients` | The maximum number of tracked usernames that have failed login. This limits heap usage to avoid a potential DoS. |
### IP address rate limiting
This configuration limits login attempts by IP address. When a login fails, the IP address specific to the machine being used for login is blocked.
There are two steps for configuring IP address rate limiting. First, set the `challenge` setting to `false` in the `http_authenticator` section of the `config.yml` file.
```yml
http_authenticator:
type: basic
challenge: false
```
For more information about this setting, see [HTTP basic authentication](#http-basic-authentication).
Second, configure the IP address rate limiting settings. The following example shows a completed configuration:
```yml
auth_failure_listeners:
ip_rate_limiting:
type: ip
allowed_tries: 1
time_window_seconds: 20
block_expiry_seconds: 180
max_blocked_clients: 100000
max_tracked_clients: 100000
```
{% include copy.html %}
The following table describes the individual settings for this type of configuration.
| Setting | Description |
| :--- | :--- |
| `type` | The type of rate limiting. In this case, `ip`. |
| `allowed_tries` | The number of login attempts allowed before login is blocked. Be aware that increasing the number increases heap usage. |
| `time_window_seconds` | The window of time in which the value for `allowed_tries` is enforced. For example, if `allowed_tries` is `3` and `time_window_seconds` is `60`, an IP address has three attempts to log in successfully within a 60-second time span before login is blocked. |
| `block_expiry_seconds` | The duration of time that login remains blocked after a failed login. After this time elapses, login is reset and the IP address can attempt successful login again. |
| `max_blocked_clients` | The maximum number of blocked IP addresses. This limits heap usage to avoid a potential DoS. |
| `max_tracked_clients` | The maximum number of tracked IP addresses that have failed login. This limits heap usage to avoid a potential DoS. |
The default `config/opensearch-security/config.yml` file included in your OpenSearch distribution contains many configuration examples. Use these examples as a starting point and customize them to your needs.
To learn about configuring supported authentication backends, see the relevant topic for each type in the [Authentication backends]({{site.url}}{{site.baseurl}}/security/authentication-backends/) documentation.
<!--- Remvoving Kerberos documentation until issue #907 is resolved.
Kerberos authentication does not work with OpenSearch Dashboards. To track OpenSearch's progress in adding support for Kerberos in OpenSearch Dashboards, see [issue #907](https://github.com/opensearch-project/security-dashboards-plugin/issues/907) in the Dashboard's Security plugin repository.
-`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:
```yml
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 [HTTP Basic Authentication](#http-basic), 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.
