31. Java Authentication and Authorization Service (JAAS) Provider
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## 31. Java Authentication and Authorization Service (JAAS) Provider

## 31.1 Overview

Spring Security provides a package able to delegate authentication requests to the Java Authentication and Authorization Service (JAAS). This package is discussed in detail below.

## 31.2 AbstractJaasAuthenticationProvider

The `AbstractJaasAuthenticationProvider` is the basis for the provided JAAS `AuthenticationProvider` implementations. Subclasses must implement a method that creates the `LoginContext`. The `AbstractJaasAuthenticationProvider` has a number of dependencies that can be injected into it that are discussed below.

### 31.2.1 JAAS CallbackHandler

Most JAAS `LoginModule` s require a callback of some sort. These callbacks are usually used to obtain the username and password from the user.

In a Spring Security deployment, Spring Security is responsible for this user interaction (via the authentication mechanism). Thus, by the time the authentication request is delegated through to JAAS, Spring Security’s authentication mechanism will already have fully-populated an `Authentication` object containing all the information required by the JAAS `LoginModule`.

Therefore, the JAAS package for Spring Security provides two default callback handlers, `JaasNameCallbackHandler` and `JaasPasswordCallbackHandler`. Each of these callback handlers implement `JaasAuthenticationCallbackHandler`. In most cases these callback handlers can simply be used without understanding the internal mechanics.

For those needing full control over the callback behavior, internally `AbstractJaasAuthenticationProvider` wraps these `JaasAuthenticationCallbackHandler` s with an `InternalCallbackHandler`. The `InternalCallbackHandler` is the class that actually implements JAAS normal `CallbackHandler` interface. Any time that the JAAS `LoginModule` is used, it is passed a list of application context configured `InternalCallbackHandler` s. If the `LoginModule` requests a callback against the `InternalCallbackHandler` s, the callback is in-turn passed to the `JaasAuthenticationCallbackHandler` s being wrapped.

### 31.2.2 JAAS AuthorityGranter

JAAS works with principals. Even "roles" are represented as principals in JAAS. Spring Security, on the other hand, works with `Authentication` objects. Each `Authentication` object contains a single principal, and multiple `GrantedAuthority` s. To facilitate mapping between these different concepts, Spring Security’s JAAS package includes an `AuthorityGranter` interface.

An `AuthorityGranter` is responsible for inspecting a JAAS principal and returning a set of `String` s, representing the authorities assigned to the principal. For each returned authority string, the `AbstractJaasAuthenticationProvider` creates a `JaasGrantedAuthority` (which implements Spring Security’s `GrantedAuthority` interface) containing the authority string and the JAAS principal that the `AuthorityGranter` was passed. The `AbstractJaasAuthenticationProvider` obtains the JAAS principals by firstly successfully authenticating the user’s credentials using the JAAS `LoginModule`, and then accessing the `LoginContext` it returns. A call to `LoginContext.getSubject().getPrincipals()` is made, with each resulting principal passed to each `AuthorityGranter` defined against the `AbstractJaasAuthenticationProvider.setAuthorityGranters(List)` property.

Spring Security does not include any production `AuthorityGranter` s given that every JAAS principal has an implementation-specific meaning. However, there is a `TestAuthorityGranter` in the unit tests that demonstrates a simple `AuthorityGranter` implementation.

## 31.3 DefaultJaasAuthenticationProvider

The `DefaultJaasAuthenticationProvider` allows a JAAS `Configuration` object to be injected into it as a dependency. It then creates a `LoginContext` using the injected JAAS `Configuration`. This means that `DefaultJaasAuthenticationProvider` is not bound any particular implementation of `Configuration` as `JaasAuthenticationProvider` is.

### 31.3.1 InMemoryConfiguration

In order to make it easy to inject a `Configuration` into `DefaultJaasAuthenticationProvider`, a default in-memory implementation named `InMemoryConfiguration` is provided. The implementation constructor accepts a `Map` where each key represents a login configuration name and the value represents an `Array` of `AppConfigurationEntry` s. `InMemoryConfiguration` also supports a default `Array` of `AppConfigurationEntry` objects that will be used if no mapping is found within the provided `Map`. For details, refer to the class level javadoc of `InMemoryConfiguration`.

### 31.3.2 DefaultJaasAuthenticationProvider Example Configuration

While the Spring configuration for `InMemoryConfiguration` can be more verbose than the standarad JAAS configuration files, using it in conjuction with `DefaultJaasAuthenticationProvider` is more flexible than `JaasAuthenticationProvider` since it not dependant on the default `Configuration` implementation.

An example configuration of `DefaultJaasAuthenticationProvider` using `InMemoryConfiguration` is provided below. Note that custom implementations of `Configuration` can easily be injected into `DefaultJaasAuthenticationProvider` as well.

    <bean id="jaasAuthProvider"
    class="org.springframework.security.authentication.jaas.DefaultJaasAuthenticationProvider">
    <property name="configuration">
    <bean class="org.springframework.security.authentication.jaas.memory.InMemoryConfiguration">
    <constructor-arg>
    	<map>
    	<!--
    	SPRINGSECURITY is the default loginContextName
    	for AbstractJaasAuthenticationProvider
    	-->
    	<entry key="SPRINGSECURITY">
    	<array>
    	<bean class="javax.security.auth.login.AppConfigurationEntry">
    		<constructor-arg value="sample.SampleLoginModule" />
    		<constructor-arg>
    		<util:constant static-field=
    			"javax.security.auth.login.AppConfigurationEntry$LoginModuleControlFlag.REQUIRED"/>
    		</constructor-arg>
    		<constructor-arg>
    		<map></map>
    		</constructor-arg>
    		</bean>
    	</array>
    	</entry>
    	</map>
    	</constructor-arg>
    </bean>
    </property>
    <property name="authorityGranters">
    <list>
    	<!-- You will need to write your own implementation of AuthorityGranter -->
    	<bean class="org.springframework.security.authentication.jaas.TestAuthorityGranter"/>
    </list>
    </property>
    </bean>

## 31.4 JaasAuthenticationProvider

The `JaasAuthenticationProvider` assumes the default `Configuration` is an instance of ConfigFile. This assumption is made in order to attempt to update the `Configuration`. The `JaasAuthenticationProvider` then uses the default `Configuration` to create the `LoginContext`.

Let’s assume we have a JAAS login configuration file, `/WEB-INF/login.conf`, with the following contents:

    JAASTest {
    	sample.SampleLoginModule required;
    };

Like all Spring Security beans, the `JaasAuthenticationProvider` is configured via the application context. The following definitions would correspond to the above JAAS login configuration file:

    <bean id="jaasAuthenticationProvider"
    class="org.springframework.security.authentication.jaas.JaasAuthenticationProvider">
    <property name="loginConfig" value="/WEB-INF/login.conf"/>
    <property name="loginContextName" value="JAASTest"/>
    <property name="callbackHandlers">
    <list>
    <bean
    	class="org.springframework.security.authentication.jaas.JaasNameCallbackHandler"/>
    <bean
    	class="org.springframework.security.authentication.jaas.JaasPasswordCallbackHandler"/>
    </list>
    </property>
    <property name="authorityGranters">
    	<list>
    	<bean class="org.springframework.security.authentication.jaas.TestAuthorityGranter"/>
    	</list>
    </property>
    </bean>

## 31.5 Running as a Subject

If configured, the `JaasApiIntegrationFilter` will attempt to run as the `Subject` on the `JaasAuthenticationToken`. This means that the `Subject` can be accessed using:

    Subject subject = Subject.getSubject(AccessController.getContext());

This integration can easily be configured using the jaas-api-provision attribute. This feature is useful when integrating with legacy or external API’s that rely on the JAAS Subject being populated.

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