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Complexity is the price of flexibility. There are several interacting system artifacts, the components and their configurations.

Spring Security itself and the CSF components are all configured using the Spring context. Configurations for Spring Security and framework components related to it are found in the applicationContext-common-security.xml of an application or in CSF. Some configuration entries in web.xml and applicationContext-web.xml are also important. When you look at the entries in these files there are many more than what are described in this document, however, it is unusual to have to change entries not discussed.

The configuration bean for the filter chain is called the filterChainProxy. Here is a sample configuration:

{code

}
	<bean id="filterChainProxy" class="org.springframework.security.web.FilterChainProxy">
        <security:filter-chain-map path-type="ant">
           <security:filter-chain pattern="/css/**" filters="logoutFilter" />
           <security:filter-chain pattern="/img/**" filters="logoutFilter" />
           <security:filter-chain pattern="/js/**" filters="logoutFilter" />
           <security:filter-chain pattern="/docs/**" filters="logoutFilter" />
           <security:filter-chain pattern="/**" filters="httpSessionContextIntegrationFilter,
           		logoutFilter,
           		ssoAuthenticationProcessingFilter,
           		basicAuthenticationProcessingFilter,
           		exceptionTranslationFilter,
           		filterSecurityInterceptor,
           		switchUserProcessingFilter"
           />
        </security:filter-chain-map>
	</bean>
{code}
In this example,

# We are telling the filter chain to run, that is authenticate and authorize, on url patterns that match everything except the contents of /images, /js, /css, and /docs.

# We are constructing the filter chain components processing order. The components are references to beans defined in the Spring context.

The beans in this example serve the following functions :

* *httpSessionContextIntegrationFilter*: Gets an existing security context from the HTTP session, or creates a new empty context.

* *ssoAuthenticationProcessingFilter*: If authentication has not already been established in the SecurityContext ( that is, was not present in the session ), checks to see if the user is already set in the servlet request, indicating that SSO has authenticated the user.

  If so, it sets up all the data structures needed by the security context. This includes the list of roles that the user is authorized for, based on the results of calling the configured authorization services ( see below ).

* *basicAuthenticationProcessingFilter*: If authentication has not already been established ( that is by either being present in the session or by SSO ), and the local.authentication property has been set, performs HTTP Basic authentication. The user is prompted for a username and password, which must match what is configured in the application property file.

  This filter is intended as a solution to running the application with a security context in the absence of SSO, which is the situation on developer's local workstations. This filter checks that the user and password entered in the login prompt in the browser match the property values for *Local Authentication Properties*. It then sets up all the data structures needed by the security context. This includes the list of roles that the user is authorized for, based on the results of calling the configured authorization services ( see below ).

* *Local Authentication Properties*: A set of CSF properties that can be used to directly set the user and roles in local development environments.

\\
\\
local.authentication=true

local.user.name=beaver

local.user.password=whatever

\\
\\
All of the above properties must be present to set a user.  The local authentication properties should never be set on Education Systems servers.
They are set in the Application Property File that resides in the user's home folder.
\\
\\
Roles may be set also, here is an example:
\\
\\
local.mitroles = WTW_REPORT_ADMIN \| 1 5 21W, WTW_READ
\\
\\
This sets two roles, WTW_REPORT_ADMIN and WTW_READ, and also sets qualifier codes 1, 5, and 21W on WTW_REPORT_ADMIN. The meaning of qualifier codes is role dependent, and some roles have no qualifiers. In this case the qualifiers represent departments that the user has this role for.

\\
\\
Only MIT roles database roles may be set this way. Other roles like instructor and student are best set by setting the user as shown above to a student or instructor.

* *exceptionTranslationFilter*: catches all exceptions from the filters that follow. Applies configured exception handlers based on the exception type caught. For example, if an AuthenticationException is thrown, indicating that the request is not authenticated yet, then it calls the method to start the authentication process.  If an AccessDeniedException is thrown, indicating that the user is not authorized, then the AccessDeniedHandler is called.

* *filterSecurityInterceptor*: Secures the requested HTTP resource(s) based on the SecurityContext. The work is delegated to a number of helpers configured for this bean. Requires a definition of what resources are to be protected and what roles apply. If the requested resource is supposed to be protected and there is no established authentication in the SecurityContext by this point, it throws an AuthenticationException which is handled as described before.  Otherwise, it will determine if authorization in the SecurityContext is sufficient for access to the resource, throwing AccessDeniedException if appropriate. 

There are several other filters in the CSF.

It is not uncommon for applications to need access to roles information that may be collected by Spring Security and the CSF. CSF provides facilities to make this easier.

*IMPORTANT*: when you are writing Java code that needs authorization information about the current user, use the methods on the CSF "SecurityContextService" interface rather than using Spring Security classes. This will insulate us from any future changes in the Spring Security framework classes.

Lets take the example of an application that needs to display a list of sections for the user to choose, which will allow them to view the students assigned to the section, and there is a rule that the class lists are only to be shown to instructors of the section.

First, we need to configure the authorization service to capture whether the user is an instructor.

{code

}
 <bean id="mitAuthorizationUserDetailService" class="edu.mit.csf.security.spring.userdetails.MitAuthorizationUserDetailsService">
	<property name="authorizationService"  ref="authorizationService" />
 </bean>

 <bean id="authorizationService" class="edu.mit.common.security.authorization.InstructorAuthorizationsService">
        <property name="dao" ref="hibernateAuthorizedInstructorDao" />
 </bean>
{code}

In this example, the instructorAuthorizationsService and hibernateAuthorizedInstructorDao bean are Spring beans defined elsewhere. The InstructorAuthorizationService has a single method, getAuthorizationsByUser. This method uses the dao to fetch the user's instructor records as an AuthorizedInstructor object containing a collection of AuthorizedTeachingAssignment objects. This is wrapped in an InstructorRoleAuthorization object which is an adaptor for communicating with Spring Security. All of this is done merely by creating the configuration above.

A little later in the application processing, we will have a list of sections, and we want to filter the list to only include those that the instructor has taught. Probably first you would want to check that the user is in fact an instructor, that is, has at least taught

 some section  at some time, and if not, perhaps show them a different page:

{code

}
boolean isInstructor = securityContextService.hasAnyRole(new String[] { InstructorRoleAuthorization.ROLE_INSTRUCTOR });

if ( isInstructor ) {

  Set allowedSections = securityContextService.getMaskedQualifiersForRole(InstructorRoleAuthorization.ROLE_INSTRUCTOR, allSections);
  // put allowedSections in model map ...

} else {
 // not so fast buster !
}
{code}

The mask method takes a collection of things that might be associated with a role and returns a set of things that actually are associated with the role. The things you can filter this way depends on the kind of role. For instructors, you can filter collections of subjects, sections, or teaching assignments. For MIT Roles Database roles that have qualifiers you can filter a collection of strings that would match the qualifier codes.