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About this document

This document is a brief description of the processing that occurs to authenticate and authorize an HTTP request using Spring Security and the CSF, highlighting features that are useful for application developers to know about.

The processing has two parts. One part is performed by Spring Security, and the other part is performed by CSF code.

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Spring Security

Spring Security is part of the Spring Framework and it abstracts authentication and authorization processing in a manner that allows them to be customized for a particular set of requirements. For web applications, Spring Security is "plugged in" as a servlet filter. If the Spring Security servlet filter is configured in the web.xml then Spring Security will be called on each request to the servlet.

Spring Security processing is composed of parts that are assembled into what is called a "filter chain". Those parts are themselves customized by injection of service beans. The filters in an Spring Security filter chain are not the same as servlet filters, although the general concept is the same. The filter chain determines the sequence of authorization and authentication processing, and the inclusion of authentication protocols.

The end result of running the filter chain is that access is either granted or denied to the resource requested. Granted access creates an Spring Security Security Context for the request, which an application may consult for roles and user information collected previously during the Spring Security processing. Denied access should cause an access denied message to be returned to the user.

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CSF

The CSF provides a wrapper around Spring Security, so that applications are not directly tied to a particular security framework implementation. It also provides services to the Spring Security filter chain that handle the specifics of authentication and authorization as are customary or required at MIT. For example, it provides services for SSO authentication, and the following services to obtain roles either separately or in combination :

MIT Roles database
Student role
Instructor role
STV_ROLES
STVACC roles

With potentially many more possibilities.

It also provides an impersonation function that is useful during testing and problem diagnosis.

It also provides local development environments a way to test different roles and users with an application.

...

*

mitAuthorizationUserDetailService

*

bean:

acts

as

an

adapter

between

the

Spring

Security

security

system

and

the

authorization

classes

in

CSF.

*

authorizationService

*

bean:

CSF

bean

that

implements

the

*

AuthorizationService

*

interface.

In

this

example,

it

is

an

implementation

that

delegates

to

a

chain

of

other

AuthorizationService

implementations,

one

for

determining

if

the

user

is

a

student,

and

another

to

obtain

the

roles

the

user

may

have

in

the

MIT

Roles

database.

The

combine

=

false

property

means

that

roles

from

the

two

services

will

not

be

combined,

that

is,

either

the

role

student

will

be

assigned

to

the

user

or

the

MIT

roles,

but

not

both.

If

combine

=

true

the

user

would

be

assigned

all

roles

found.

[

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The Authorization Framework

As mentioned above, filters that authenticate users also get the "details" for the authenticated user, that is, the user's authorizations, to put into the security context. In CSF, there is a single bean that is configured to get the user details, the mitAuthorizationUserDetailService.

Here is a sample configuration:

Code Block

    <!-- the Spring Security adapter for MIT authorizations retrieval -->
    <bean id="mitAuthorizationUserDetailService" class="edu.mit.csf.security.spring.userdetails.MitAuthorizationUserDetailsService">
        <property name="authorizationService" ref="authorizationService"/>
    </bean>

    <!-- MIT Roles database authorization -->
    <bean id="mitRolesAuthorizationService" class="edu.mit.csf.security.service.MitRolesAuthorizationService">
        <property name="applicationConfiguration" ref="applicationConfiguration" />
        <property name="uaSao" ref="uaSao" />
        <!-- all the academic services apps use this domain, same as category in MIT Roles -->
        <property name="domain" value="REG" />
        <!-- if you have this property value in your applicationConfiguration then
        getDomain be overridden with the value this property -->
        <property name="domainProperty" value="roles.function.category"/>
        <property name="functionProperty" value="roles.function.function"/>
    </bean>

The beans and property definitions in this example serve the following functions:

Code Block

}

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Application access to a user's roles in the Security Context

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 Block


 <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>

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 Block


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 !
}

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.

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Impersonation

Impersonation that is a regular part of an application's feature set delivered to MIT administrators is accomplished with an additional filter on the Spring Security filter chain called the switchProcessingUserFilter.This basically gives authorized users a "login" button or link that logs them in as another user. Once the switch is performed, the SecurityContext contains the credentials for a different user, but it also remembers the original user so impersonation may be exited and the original credentials restored.

There are a couple of things that are required to use this filter.

There must be a role, usually in the MIT Roles database, associated with users allowed to do the impersonation.
The login url should be protected at the page level with this role. Third, the login url, and a logout url, should be implemented and configured on the filter. Fourth, the filter should be added to the filterChainProxy bean configuration, after the filterSecurityInterceptor, since we have to get the "can impersonate" role first. ( Example TBD )

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Page level security

One may also configure a mapping of roles to page urls. In the example above where we were testing if a user had the instructor role before showing them a page to select sections to view, instead of writing code, we could have declared our protection like this:

Code Block


	<bean id="filterSecurityInterceptor" class="org.springframework.security.web.access.intercept.FilterSecurityInterceptor">
		<property name="authenticationManager" ref="authenticationManager"/>
		<property name="accessDecisionManager" ref="accessDecisionManager"/>
                <property name="securityMetadataSource">
                   <security:filter-security-metadata-source>
                         <security:intercept-url pattern="/advisor_reg_summary.htm" access="ROLE_OREG_REGISTRAR,ROLE_OREG_DEPT_ADMIN,ROLE_OREG_ADVISOR" />
                         <security:intercept-url pattern="/agreement.htm" access="ROLE_CURRENT_STUDENT" />
                   </security:filter-security-metadata-source>
                </property>
        </bean>

and the Spring Security framework would have invoked the access denied handler when a user who did not have this role tried to access the page. We could then write the access denied handler to show a page with a friendly message or perhaps redirect the user somewhere they are supposed to be instead.

The "pattern" attributes specify which URL(s) are to be restricted. Patterns can specify a specific page, as in the above examples, or can specify a range of URLs via wildcards. For example, the following pattern would restrict all pages under the "admin" folder to users with the "ADMIN" role:

Code Block
<security:intercept-url pattern="/admin/*" access="ROLE_ADMIN" />

Overlapping patterns can also be specified: the latter-defined patterns will override the earlier patterns. An example of this usage would be a section of a web site generally restricted to DINING users, but with certain pages also open to REGISTRAR users. We would define a general pattern to implement the DINING users restriction, and a second more specific pattern giving the REGISTRAR users access to particular pages:

Code Block
<security:intercept-url pattern="/dining/*" access="ROLE_DINING" /> <security:intercept-url pattern="/dining/some_shared_page.htm" access="ROLE_DINING,ROLE_REGISTRAR" />

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Key

About this document

Spring Security

CSF

The Authorization Framework

Application access to a user's roles in the Security Context

Impersonation

Page level security