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<?oxygen RNGSchema="http://www.oasis-open.org/docbook/xml/5.0/rng/docbook.rng" type="xml"?>
<article class="faq" xml:id="spring-security-faq" xmlns="http://docbook.org/ns/docbook"
    xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0">
    <info>
        <title>Frequently Answered Questions (FAQ)</title>
    </info>
    <section>
        <title>General Questions</title>
        <qandaset>
            <qandadiv>
                <qandaentry xml:id="faq-other-concerns">
                    <question>
                        <para>Will Spring Security take care of all my application security
                            requirements?</para>
                    </question>
                    <answer>
                        <para> Spring Security provides you with a very flexible framework for your
                            authentication and authorization requirements, but there are many other
                            considerations for building a secure application that are outside its
                            scope. Web applications are vulnerable to all kinds of attacks which you
                            should be familiar with, preferably before you start development so you
                            can design and code with them in mind from the beginning. Check out the
                            <link xlink:href="http://www.owasp.org/">OWASP web site</link> for
                            information on the major issues facing web application developers and
                            the countermeasures you can use against them.</para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-web-xml">
                    <question>
                        <para>Why not just use web.xml security?</para>
                    </question>
                    <answer>
                        <para>Let's assume you're developing an enterprise application based on
                            Spring. There are four security concerns you typically need to address:
                            authentication, web request security, service layer security (i.e. your
                            methods that implement business logic), and domain object instance
                            security (i.e. different domain objects have different permissions).
                            With these typical requirements in mind: <orderedlist>
                            <listitem>
                                <para><emphasis>Authentication</emphasis>: The servlet specification
                                    provides an approach to authentication. However, you will need
                                    to configure the container to perform authentication which
                                    typically requires editing of container-specific "realm"
                                    settings. This makes a non-portable configuration, and if you
                                    need to write an actual Java class to implement the container's
                                    authentication interface, it becomes even more non-portable.
                                    With Spring Security you achieve complete portability - right
                                    down to the WAR level. Also, Spring Security offers a choice of
                                    production-proven authentication providers and mechanisms,
                                    meaning you can switch your authentication approaches at
                                    deployment time. This is particularly valuable for software
                                    vendors writing products that need to work in an unknown target
                                    environment.</para>
                            </listitem>
                            <listitem>
                                <para><emphasis>Web request security:</emphasis> The servlet
                                    specification provides an approach to secure your request URIs.
                                    However, these URIs can only be expressed in the servlet
                                    specification's own limited URI path format. Spring Security
                                    provides a far more comprehensive approach. For instance, you
                                    can use Ant paths or regular expressions, you can consider parts
                                    of the URI other than simply the requested page (e.g. you can
                                    consider HTTP GET parameters) and you can implement your own
                                    runtime source of configuration data. This means your web
                                    request security can be dynamically changed during the actual
                                    execution of your webapp.</para>
                            </listitem>
                            <listitem>
                                <para><emphasis>Service layer and domain object security:</emphasis>
                                    The absence of support in the servlet specification for services
                                    layer security or domain object instance security represent
                                    serious limitations for multi-tiered applications. Typically
                                    developers either ignore these requirements, or implement
                                    security logic within their MVC controller code (or even worse,
                                    inside the views). There are serious disadvantages with this
                                    approach: <orderedlist>
                                    <listitem>
                                        <para><emphasis>Separation of concerns:</emphasis>
                                            Authorization is a crosscutting concern and should be
                                            implemented as such. MVC controllers or views
                                            implementing authorization code makes it more difficult
                                            to test both the controller and authorization logic,
                                            more difficult to debug, and will often lead to code
                                            duplication.</para>
                                    </listitem>
                                    <listitem>
                                        <para><emphasis>Support for rich clients and web
                                            services:</emphasis> If an additional client type must
                                            ultimately be supported, any authorization code embedded
                                            within the web layer is non-reusable. It should be
                                            considered that Spring remoting exporters only export
                                            service layer beans (not MVC controllers). As such
                                            authorization logic needs to be located in the services
                                            layer to support a multitude of client types.</para>
                                    </listitem>
                                    <listitem>
                                        <para><emphasis>Layering issues:</emphasis> An MVC
                                            controller or view is simply the incorrect architectural
                                            layer to implement authorization decisions concerning
                                            services layer methods or domain object instances.
                                            Whilst the Principal may be passed to the services layer
                                            to enable it to make the authorization decision, doing
                                            so would introduce an additional argument on every
                                            services layer method. A more elegant approach is to use
                                            a ThreadLocal to hold the Principal, although this would
                                            likely increase development time to a point where it
                                            would become more economical (on a cost-benefit basis)
                                            to simply use a dedicated security framework.</para>
                                    </listitem>
                                    <listitem>
                                        <para><emphasis>Authorisation code quality:</emphasis> It is
                                            often said of web frameworks that they "make it easier
                                            to do the right things, and harder to do the wrong
                                            things". Security frameworks are the same, because they
                                            are designed in an abstract manner for a wide range of
                                            purposes. Writing your own authorization code from
                                            scratch does not provide the "design check" a framework
                                            would offer, and in-house authorization code will
                                            typically lack the improvements that emerge from
                                            widespread deployment, peer review and new versions.
                                        </para>
                                    </listitem>
                                    </orderedlist></para>
                            </listitem>
                            </orderedlist></para>
                        <para> For simple applications, servlet specification security may just be
                            enough. Although when considered within the context of web container
                            portability, configuration requirements, limited web request security
                            flexibility, and non-existent services layer and domain object instance
                            security, it becomes clear why developers often look to alternative
                            solutions. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-requirements">
                    <question>
                        <para>What Java and Spring Framework versions are required?</para>
                    </question>
                    <answer>
                        <para> Spring Security 3.0 and 3.1 require at least JDK 1.5 and also
                            require Spring 3.0.3 as a minimum. Ideally you should be using the latest
                            release versions to avoid problems.
                        </para>
                        <para> Spring Security 2.0.x requires a minimum JDK version of 1.4 and is
                            built against Spring 2.0.x. It should also be compatible with
                            applications using Spring 2.5.x. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-start-simple">
                    <question>
                        <para> I'm new to Spring Security and I need to build an application that
                            supports CAS single sign-on over HTTPS, while allowing Basic
                            authentication locally for certain URLs, authenticating against multiple
                            back end user information sources (LDAP and JDBC). I've copied some
                            configuration files I found but it doesn't work. What could be wrong? </para>
                        <para>Or subsititute an alternative complex scenario...</para>
                    </question>
                    <answer>
                        <para> Realistically, you need an understanding of the technolgies you are
                            intending to use before you can successfully build applications with
                            them. Security is complicated. Setting up a simple configuration using a
                            login form and some hard-coded users using Spring Security's namespace
                            is reasonably straightforward. Moving to using a backed JDBC database is
                            also easy enough. But if you try and jump straight to a complicated
                            deployment scenario like this you will almost certainly be frustrated.
                            There is a big jump in the learning curve required to set up systems
                            like CAS, configure LDAP servers and install SSL certificates properly.
                            So you need to take things one step at a time. </para>
                        <para> From a Spring Security perspective, the first thing you should do is
                            follow the <quote>Getting Started</quote> guide on the web site. This
                            will take you through a series of steps to get up and running and get
                            some idea of how the framework operates. If you are using other
                            technologies which you aren't familiar with then you should do some
                            research and try to make sure you can use them in isolation before
                            combining them in a complex system. </para>
                    </answer>
                </qandaentry>
            </qandadiv>
        </qandaset>
    </section>
    <section>
        <title>Common Problems</title>
        <qandaset>
            <qandadiv>
                <title>Authentication</title>
                <qandaentry xml:id="faq-bad-credentials">
                    <question>
                        <para>When I try to log in, I get an error message that says "Bad
                            Credentials". What's wrong?</para>
                    </question>
                    <answer>
                        <para>This means that authentication has failed. It doesn't say why, as it
                            is good practice to avoid giving details which might help an attacker
                            guess account names or passwords.</para>
                        <para>This also means that if you ask this question in the forum, you will
                            not get an answer unless you provide additional information. As with any
                            issue you should check the output from the debug log, note any exception
                            stacktraces and related messages. Step through the code in a debugger to
                            see where the authentication fails and why. Write a test case which
                            exercises your authentication configuration outside of the application.
                            More often than not, the failure is due to a difference in the password
                            data stored in a database and that entered by the user. If you are using
                            hashed passwords, make sure the value stored in your database is
                            <emphasis>exactly</emphasis> the same as the value produced by the
                            <interfacename>PasswordEncoder</interfacename> configured in your
                            application.</para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-login-loop">
                    <question>
                        <para>My application goes into an "endless loop" when I try to login, what's
                            going on?</para>
                    </question>
                    <answer>
                        <para>A common user problem with infinite loop and redirecting to the login
                            page is caused by accidently configuring the login page as a "secured"
                            resource. Make sure your configuration allows anonymous access to the
                            login page, either by excluding it from the security filter chain or
                            marking it as requiring ROLE_ANONYMOUS.</para>
                        <para>If your AccessDecisionManager includes an AuthenticatedVoter, you can
                            use the attribute "IS_AUTHENTICATED_ANONYMOUSLY". This is automatically
                            available if you are using the standard namespace configuration setup. </para>
                        <para> From Spring Security 2.0.1 onwards, when you are using
                            namespace-based configuration, a check will be made on loading the
                            application context and a warning message logged if your login page
                            appears to be protected. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-anon-access-denied">
                    <question>
                        <para>I get an exception with the message "Access is denied (user is
                            anonymous);". What's wrong?</para>
                    </question>
                    <answer>
                        <para> This is a debug level message which occurs the first time an
                            anonymous user attempts to access a protected resource.
                            <programlisting>
    DEBUG [ExceptionTranslationFilter] - Access is denied (user is anonymous); redirecting to authentication entry point
    org.springframework.security.AccessDeniedException: Access is denied
    at org.springframework.security.vote.AffirmativeBased.decide(AffirmativeBased.java:68)
    at org.springframework.security.intercept.AbstractSecurityInterceptor.beforeInvocation(AbstractSecurityInterceptor.java:262)
                </programlisting>
                            It is normal and shouldn't be anything to worry about. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-cached-secure-page">
                    <question>
                        <para>Why can I still see a secured page even after I've logged out of my
                            application?</para>
                    </question>
                    <answer>
                        <para>The most common reason for this is that your browser has cached the
                            page and you are seeing a copy which is being retrieved from the
                            browsers cache. Verify this by checking whether the browser is actually
                            sending the request (check your server access logs, the debug log or use
                            a suitable browser debugging plugin such as <quote>Tamper Data</quote>
                            for Firefox). This has nothing to do with Spring Security and you should
                            configure your application or server to set the appropriate
                            <literal>Cache-Control</literal> response headers. Note that SSL
                            requests are never cached.</para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="auth-exception-credentials-not-found">
                    <question>
                        <para>I get an exception with the message "An Authentication object was not
                            found in the SecurityContext". What's wrong?</para>
                    </question>
                    <answer>
                        <para> This is a another debug level message which occurs the first time an
                            anonymous user attempts to access a protected resource, but when you do
                            not have an <classname>AnonymousAuthenticationFilter</classname> in your
                            filter chain configuration.
                            <programlisting>
    DEBUG [ExceptionTranslationFilter] - Authentication exception occurred; redirecting to authentication entry point
    org.springframework.security.AuthenticationCredentialsNotFoundException:
                   An Authentication object was not found in the SecurityContext
    at org.springframework.security.intercept.AbstractSecurityInterceptor.credentialsNotFound(AbstractSecurityInterceptor.java:342)
    at org.springframework.security.intercept.AbstractSecurityInterceptor.beforeInvocation(AbstractSecurityInterceptor.java:254)
                </programlisting>
                            It is normal and shouldn't be anything to worry about. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-ldap-authentication">
                    <question><para>I can't get LDAP authentication to work. What's wrong with my configuration?</para></question>
                    <answer>
                        <para>
                            Note that the permissions for an LDAP directory often do not allow you to read the password
                            for a user. Hence it is often not possible to use the <link xlink:href="#faq-what-is-userdetailservice"><interfacename>UserDetailsService</interfacename>
                            approach</link> where Spring Security compares the stored password with the one submitted by the user.
                            The most common approach is to use LDAP <quote>bind</quote>, which is one of the operations
                            supported by <link xlink:href="http://en.wikipedia.org/wiki/Lightweight_Directory_Access_Protocol">the LDAP protocol</link>.
                            With this approach, Spring Security validates the password by attempting to authenticate to the directory
                            as the user.
                        </para>
                        <para>The most common problem with LDAP authentication is a lack of knowledge of the
                            directory server tree structure and configuration. This will be different in different
                            companies, so you have to find it out yourself. Before adding a Spring Security LDAP
                            configuration to an application, it's a good idea to write a simple test using standard
                            Java LDAP code (without Spring Security involved), and make sure you can
                            get that to work first. For example, to authenticate a user, you could use
                            the following code:
                            <programlisting language="java"><![CDATA[
    @Test
    public void ldapAuthenticationIsSuccessful() throws Exception {
        Hashtable<String,String> env = new Hashtable<String,String>();
        env.put(Context.SECURITY_AUTHENTICATION, "simple");
        env.put(Context.SECURITY_PRINCIPAL, "cn=joe,ou=users,dc=mycompany,dc=com");
        env.put(Context.PROVIDER_URL, "ldap://mycompany.com:389/dc=mycompany,dc=com");
        env.put(Context.SECURITY_CREDENTIALS, "joespassword");
        env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");

        InitialLdapContext ctx = new InitialLdapContext(env, null);

    }
    ]]></programlisting>
                        </para>
                    </answer>
                </qandaentry>

            </qandadiv>
            <qandadiv xml:id="faq-session-management">
                <title>Session Management</title>
                <para> Session management issues are a common source of forum questions. If you are
                    developing Java web applications, you should understand how the session is
                    maintained between the servlet container and the user's browser. You should also
                    understand the difference between secure and non-secure cookies and the
                    implications of using HTTP/HTTPS and switching between the two. Spring Security
                    has nothing to do with maintaining the session or providing session identifiers.
                    This is entirely handled by the servlet container. </para>

                <qandaentry xml:id="faq-concurrent-session-same-browser">
                    <question>
                        <para>I'm using Spring Security's concurrent session control to prevent
                            users from logging in more than once at a time. When I open another
                            browser window after logging in, it doesn't stop me from logging in
                            again. Why can I log in more than once? </para>
                    </question>
                    <answer>
                        <para>Browsers generally maintain a single session per browser instance. You
                            cannot have two separate sessions at once. So if you log in again in
                            another window or tab you are just reauthenticating in the same session.
                            The server doesn't know anything about tabs, windows or browser
                            instances. All it sees are HTTP requests and it ties those to a
                            particular session according to the value of the the JSESSIONID cookie
                            that they contain. When a user authenticates during a session, Spring
                            Security's concurrent session control checks the number of
                            <emphasis>other authenticated sessions</emphasis> that they have. If
                            they are already authenticated with the same session, then
                            re-authenticating will have no effect. </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-new-session-on-authentication">
                    <question>
                        <para>Why does the session Id change when I authenticate through Spring
                            Security?</para>
                    </question>
                    <answer>
                        <para>With the default configuration, Spring Security invalidates the
                            existing session when the user authenticates and creates a new one,
                            transferring the session data to it. The intention is to change the
                            session identifier to prevent <quote>session-fixation</quote> attacks.
                            You can find more about this online and in the reference manual. </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-tomcat-https-session">
                    <question>
                        <para> I'm using Tomcat (or some other servlet container) and have enabled
                            HTTPS for my login page, switching back to HTTP afterwards. It doesn't
                            work - I just end up back at the login page after authenticating.
                        </para>
                    </question>
                    <answer>
                        <para> This happens because sessions created under HTTPS, for which the
                            session cookie is marked as <quote>secure</quote>, cannot subsequently
                            be used under HTTP. The browser will not send the cookie back to the
                            server and any session state will be lost (including the security
                            context information). Starting a session in HTTP first should work as
                            the session cookie won't be marked as secure (you will also have to
                            disable Spring Security's <link
                            xlink:href="http://static.springsource.org/spring-security/site/docs/3.1.x/reference/springsecurity-single.html#ns-session-fixation"
                            > Session Fixation Protection</link> support to prevent it from creating
                            a new secure session on login (you can always create a new session
                            yourself at a later stage). Note that switching between HTTP and HTTPS
                            is not a good idea in general, as any application which uses HTTP at all
                            is vulnerable to man-in-the-middle attacks. To be truly secure, the user
                            should begin accessing your site in HTTPS and continue using it until
                            they log out. Even clicking on an HTTPS link from a page accessed over
                            HTTP is potentially risky. If you need more convincing, check out a tool
                            like <link xlink:href="http://www.thoughtcrime.org/software/sslstrip/"
                            >sslstrip</link>. </para>
                    </answer>
                </qandaentry>

                <qandaentry>
                    <question>
                        <para>I'm not switching between HTTP and HTTPS but my session is still
                            getting lost</para>
                    </question>
                    <answer>
                        <para>Sessions are maintained either by exchanging a session cookie or by
                            adding the a <literal>jsessionid</literal> parameter to URLs (this
                            happens automatically if you are using JSTL to output URLs, or if you
                            call <literal>HttpServletResponse.encodeUrl</literal> on URLs (before a
                            redirect, for example). If clients have cookies disabled, and you are
                            not rewriting URLs to include the <literal>jsessionid</literal>, then
                            the session will be lost. Note that the use of cookies is preferred for
                            security reasons, as it does not expose the session information in the
                            URL. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-session-listener-missing">
                    <question>
                        <para>I'm trying to use the concurrent session-control support but it won't
                            let me log back in, even if I'm sure I've logged out and haven't
                            exceeded the allowed sessions. </para>
                    </question>
                    <answer>
                        <para>Make sure you have added the listener to your web.xml file. It is
                            essential to make sure that the Spring Security session registry is
                            notified when a session is destroyed. Without it, the session
                            information will not be removed from the registry.</para>
                        <programlisting language="xml"><![CDATA[
    <listener>
        <listener-class>org.springframework.security.ui.session.HttpSessionEventPublisher</listener-class>
    </listener> ]]>
            </programlisting>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-unwanted-session-creation">
                    <question>
                        <para>Spring Security is creating a session somewhere, even though I've
                            configured it not to, by setting the <literal>create-session</literal>
                            attribute to <literal>never</literal>. </para>
                    </question>
                    <answer>
                        <para>This usually means that the user's application is creating a session
                            somewhere, but that they aren't aware of it. The most common culprit is
                            a JSP. Many people aren't aware that JSPs create sessions by default. To
                            prevent a JSP from creating a session, add the directive <literal>&lt;%@
                            page session="false" %&gt;</literal> to the top of the page. </para>
                        <para> If you are having trouble working out where a session is being
                            created, you can add some debugging code to track down the location(s).
                            One way to do this would be to add a
                            <literal>javax.servlet.http.HttpSessionListener</literal> to your
                            application, which calls <literal>Thread.dumpStack()</literal> in the
                            <literal>sessionCreated</literal> method. </para>
                    </answer>
                </qandaentry>
            </qandadiv>
            <qandadiv>
                <title>Miscellaneous</title>
                <qandaentry xml:id="faq-no-security-on-forward">
                    <question>
                        <para> I'm forwarding a request to another URL using the RequestDispatcher,
                            but my security constraints aren't being applied. </para>
                    </question>
                    <answer>
                        <para> Filters are not applied by default to forwards or includes. If you
                            really want the security filters to be applied to forwards and/or
                            includes, then you have to configure these explicitly in your web.xml
                            using the &lt;dispatcher&gt; element, a child element of
                            &lt;filter-mapping&gt;. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-method-security-in-web-context">
                    <question>
                        <para>I have added Spring Security's &lt;global-method-security&gt; element
                            to my application context but if I add security annotations to my Spring
                            MVC controller beans (Struts actions etc.) then they don't seem to have
                            an effect.</para>
                    </question>
                    <answer>
                        <para> In a Spring web application, the application context which holds the
                            Spring MVC beans for the dispatcher servlet is often separate from the
                            main application context. It is often defined in a file called
                            <literal>myapp-servlet.xml</literal>, where <quote>myapp</quote> is the
                            name assigned to the Spring <classname>DispatcherServlet</classname> in
                            <filename>web.xml</filename>. An application can have multiple
                            <classname>DispatcherServlet</classname>s, each with its own isolated
                            application context. The beans in these <quote>child</quote> contexts
                            are not visible to the rest of the application. The
                            <quote>parent</quote> application context is loaded by the
                            <classname>ContextLoaderListener</classname> you define in your
                            <filename>web.xml</filename> and is visible to all the child contexts.
                            This parent context is usually where you define your security
                            configuration, including the
                            <literal>&lt;global-method-security&gt;</literal> element). As a result
                            any security constraints applied to methods in these web beans will not
                            be enforced, since the beans cannot be seen from the
                            <classname>DispatcherServlet</classname> context. You need to either
                            move the <literal>&lt;global-method-security&gt;</literal> declaration
                            to the web context or moved the beans you want secured into the main
                            application context. </para>
                        <para>Generally we would recommend applying method security at the service
                            layer rather than on individual web controllers.</para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-no-filters-no-context">
                    <question>
                        <para>I have a user who has definitely been authenticated, but when I try to
                            access the <classname>SecurityContextHolder</classname> during some
                            requests, the <interfacename>Authentication</interfacename> is null. Why
                            can't I see the user information? </para>
                    </question>
                    <answer>
                        <para>If you have excluded the request from the security filter chain using
                            the attribute <literal>filters='none'</literal> in the
                            <literal>&lt;intercept-url></literal> element that matches the URL
                            pattern, then the <classname>SecurityContextHolder</classname> will not
                            be populated for that request. Check the debug log to see whether the
                            request is passing through the filter chain. (You are reading the debug
                            log, right?).</para>
                    </answer>
                </qandaentry>
            </qandadiv>
        </qandaset>
    </section>
    <section>
        <title>Spring Security Architecture Questions</title>
        <qandaset>
            <qandadiv>
                <qandaentry xml:id="faq-where-is-class-x">
                    <question>
                        <para>How do I know which package class X is in?</para>
                    </question>
                    <answer>
                        <para>The best way of locating classes is by installing the Spring Security
                            source in your IDE. The distribution includes source jars for each of
                            the modules the project is divided up into. Add these to your project
                            source path and you can navigate directly to Spring Security classes
                            (<command>Ctrl-Shift-T</command> in Eclipse). This also makes debugging
                            easier and allows you to troubleshoot exceptions by looking directly at
                            the code where they occur to see what's going on there. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-namespace-to-bean-mapping">
                    <question>
                        <para>How do the namespace elements map to conventional bean
                            configurations?</para>
                    </question>
                    <answer>
                        <para>There is a general overview of what beans are created by the namespace
                            in the namespace appendix of the reference guide. There is also a
                            detailed blog article called <quote>Behind the Spring Security
                            Namespace</quote> on <link
                            xlink:href="http://blog.springsource.com/2010/03/06/behind-the-spring-security-namespace/"
                            >blog.springsource.com</link>. If want to know the full details then the
                            code is in the <filename>spring-security-config</filename> module within
                            the Spring Security 3.0 distribution. You should probably read the
                            chapters on namespace parsing in the standard Spring Framework reference
                            documentation first.</para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-role-prefix">
                    <question>
                        <para>What does <quote>ROLE_</quote> mean and why do I need it on my role
                            names?</para>
                    </question>
                    <answer>
                        <para>Spring Security has a voter-based architecture which means that an
                            access decision is made by a series of
                            <interfacename>AccessDecisionVoter</interfacename>s. The voters act on
                            the <quote>configuration attributes</quote> which are specified for a
                            secured resource (such as a method invocation). With this approach, not
                            all attributes may be relevant to all voters and a voter needs to know
                            when it should ignore an attribute (abstain) and when it should vote to
                            grant or deny access based on the attribute value. The most common voter
                            is the <classname>RoleVoter</classname> which by default votes whenever
                            it finds an attribute with the <quote>ROLE_</quote> prefix. It makes a
                            simple comparison of the attribute (such as <quote>ROLE_USER</quote>)
                            with the names of the authorities which the current user has been
                            assigned. If it finds a match (they have an authority called
                            <quote>ROLE_USER</quote>), it votes to grant access, otherwise it votes
                            to deny access. </para>
                        <para> The prefix can be changed by setting the
                            <literal>rolePrefix</literal> property of
                            <classname>RoleVoter</classname>. If you only need to use roles in your
                            application and have no need for other custom voters, then you can set
                            the prefix to a blank string, in which case the
                            <classname>RoleVoter</classname> will treat all attributes as roles.
                        </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-what-dependencies">
                    <question>
                        <para>How do I know which dependencies to add to my application to work with
                            Spring Security?</para>
                    </question>
                    <answer>
                        <para>It will depend on what features you are using and what type of
                            application you are developing. With Spring Security 3.0, the project
                            jars are divided into clearly distinct areas of functionality, so it is
                            straightforward to work out which Spring Security jars you need from
                            your application requirements. All applications will need the
                            <filename>spring-security-core</filename> jar. If you're developing a
                            web application, you need the <filename>spring-security-web</filename>
                            jar. If you're using security namespace configuration you need the
                            <filename>spring-security-config</filename> jar, for LDAP support you
                            need the <filename>spring-security-ldap</filename> jar and so on. </para>
                        <para> For third-party jars the situation isn't always quite so obvious. A
                            good starting point is to copy those from one of the pre-built sample
                            applications WEB-INF/lib directories. For a basic application, you can
                            start with the tutorial sample. If you want to use LDAP, with an
                            embedded test server, then use the LDAP sample as a starting point. The
                            reference manual also includes
                            <link xlink:href="http://static.springsource.org/spring-security/site/docs/3.1.x/reference/springsecurity-single.html#appendix-dependencies">an appendix</link> listing the first-level
                            dependencies for each Spring Security module with some information on
                            whether they are optional and what they are required for. </para>
                        <para> If you are building your project with maven, then adding the
                            appropriate Spring Security modules as dependencies to your pom.xml will
                            automatically pull in the core jars that the framework requires. Any
                            which are marked as "optional" in the Spring Security POM files will
                            have to be added to your own pom.xml file if you need them. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-apacheds-deps">
                    <question><para>What dependencies are needed to run an embedded ApacheDS LDAP server?</para></question>
                    <answer><para>If you are using Maven, you need to add the folowing to your pom dependencies:<programlisting><![CDATA[
        <dependency>
            <groupId>org.apache.directory.server</groupId>
            <artifactId>apacheds-core</artifactId>
            <version>1.5.5</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.apache.directory.server</groupId>
            <artifactId>apacheds-server-jndi</artifactId>
            <version>1.5.5</version>
            <scope>runtime</scope>
        </dependency>
]]></programlisting>. The other required jars should be pulled in transitively.
                    </para></answer>
                </qandaentry>
                <qandaentry xml:id="faq-what-is-userdetailservice">
                    <question>
                        <para>What is a <interfacename>UserDetailsService</interfacename> and do I need
                            one?</para>
                    </question>
                    <answer>
                        <para><interfacename>UserDetailsService</interfacename> is a DAO interface
                            for loading data that is specific to a user account. It has no other
                            function other to load that data for use by other components within the
                            framework. It is not responsible for authenticating the user.
                            Authenticating a user with a username/password combination is most
                            commonly performed by the
                            <classname>DaoAuthenticationProvider</classname>, which is injected with
                            a <interfacename>UserDetailsService</interfacename> to allow it to load
                            the password (and other data) for a user in order to compare it with the
                            submitted value. Note that if you are using LDAP,
                            <link xlink:href="#faq-ldap-authentication">this approach may not work</link>.</para>
                        <para> If you want to customize the authentication process then you should
                            implement <interfacename>AuthenticationProvider</interfacename>
                            yourself. See this <link
                            xlink:href="http://blog.springsource.com/2010/08/02/spring-security-in-google-app-engine/"
                            > blog article</link> for an example integrating Spring Security
                            authentication with Google App Engine. </para>
                    </answer>
                </qandaentry>
            </qandadiv>
        </qandaset>
    </section>
    <section>
        <title>Common <quote>Howto</quote> Requests</title>
        <qandaset>
            <qandadiv>
                <qandaentry xml:id="faq-extra-login-fields">
                    <question>
                        <para>I need to login in with more information than just the username. How
                            do I add support for extra login fields (e.g. a company name)?</para>
                    </question>
                    <answer>
                        <para>This question comes up repeatedly in the Spring Security forum so you
                            will find more information there by searching the archives (or through
                            google).</para>
                        <para> The submitted login information is processed by an instance of
                            <classname>UsernamePasswordAuthenticationFilter</classname>. You will
                            need to customize this class to handle the extra data field(s). One
                            option is to use your own customized authentication token class (rather
                            than the standard
                            <classname>UsernamePasswordAuthenticationToken</classname>), another is
                            simply to concatenate the extra fields with the username (for example,
                            using a ":" as the separator) and pass them in the username property of
                            <classname>UsernamePasswordAuthenticationToken</classname>. </para>
                        <para> You will also need to customize the actual authentication process. If
                            you are using a custom authentication token class, for example, you will
                            have to write an <classname>AuthenticationProvider</classname> to handle
                            it (or extend the standard
                            <classname>DaoAuthenticationProvider</classname>). If you have
                            concatenated the fields, you can implement your own
                            <interfacename>UserDetailsService</interfacename> which splits them up
                            and loads the appropriate user data for authentication. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-matching-url-fragments">
                    <question>
                        <para>How do I apply different <literal>intercept-url</literal> constraints
                            where only the fragment value of the requested URLs differs (e.g.
                            <literal>/foo#bar</literal> and <literal>/foo#blah</literal>?</para>
                    </question>
                    <answer>
                        <para>You can't do this, since the fragment is not transmitted from the
                            browser to the server. The URLs above are identical from the server's
                            perspective. This is a common question from GWT users.</para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-request-details-in-user-service">
                    <question>
                        <para>How do I access the user's IP Address (or other web-request data) in a
                            <interfacename>UserDetailsService</interfacename>?</para>
                    </question>
                    <answer>
                        <para> Obviously you can't (without resorting to something like thread-local
                            variables) since the only information supplied to the interface is the
                            username. Instead of implementing
                            <interfacename>UserDetailsService</interfacename>, you should implement
                            <interfacename>AuthenticationProvider</interfacename> directly and
                            extract the information from the supplied
                            <interfacename>Authentication</interfacename> token. </para>
                        <para> In a standard web setup, the <methodname>getDetails()</methodname>
                            method on the <interfacename>Authentication</interfacename> object will
                            return an instance of <classname>WebAuthenticationDetails</classname>.
                            If you need additional information, you can inject a custom
                            <interfacename>AuthenticationDetailsSource</interfacename> into the
                            authentication filter you are using. If you are using the namespace, for
                            example with the <literal>&lt;form-login&gt;</literal> element, then you
                            should remove this element and replace it with a
                            <literal>&lt;custom-filter&gt;</literal> declaration pointing to an
                            explicitly configured
                            <classname>UsernamePasswordAuthenticationFilter</classname>. </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-access-session-from-user-service">
                    <question>
                        <para>How do I access the <interfacename>HttpSession</interfacename> from a
                            <interfacename>UserDetailsService</interfacename>?</para>
                    </question>
                    <answer>
                        <para>You can't, since the <interfacename>UserDetailsService</interfacename>
                            has no awareness of the servlet API. If you want to store custom user
                            data, then you should customize the
                            <interfacename>UserDetails</interfacename> object which is returned.
                            This can then be accessed at any point, via the thread-local
                            <classname>SecurityContextHolder</classname>. A call to
                            <literal>SecurityContextHolder.getContext().getAuthentication().getPrincipal()</literal>
                            will return this custom object. </para>
                        <para> If you really need to access the session, then it must be done by
                            customizing the web tier. </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-password-in-user-service">
                    <question>
                        <para>How do I access the user's password in a
                            <interfacename>UserDetailsService</interfacename>?</para>
                    </question>
                    <answer>
                        <para>You can't (and shouldn't). You are probably misunderstanding its purpose.
                            See <quote><link xlink:href="#faq-what-is-userdetailservice">What is a UserDetailsService?</link></quote>
                            above.
                        </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-dynamic-url-metadata">
                    <question>
                        <para>How do I define the secured URLs within an application
                            dynamically?</para>
                    </question>
                    <answer>
                        <para>People often ask about how to store the mapping between secured URLs
                            and security metadata attributes in a database, rather than in the
                            application context. </para>
                        <para> The first thing you should ask yourself is if you really need to do
                            this. If an application requires securing, then it also requires that
                            the security be tested thoroughly based on a defined policy. It may
                            require auditing and acceptance testing before being rolled out into a
                            production environment. A security-conscious organization should be
                            aware that the benefits of their diligent testing process could be wiped
                            out instantly by allowing the security settings to be modified at
                            runtime by changing a row or two in a configuration database. If you
                            have taken this into account (perhaps using multiple layers of security
                            within your application) then Spring Security allows you to fully
                            customize the source of security metadata. You can make it fully dynamic
                            if you choose. </para>
                        <para> Both method and web security are protected by subclasses of
                            <classname>AbstractSecurityInterceptor</classname> which is configured
                            with a <interfacename>SecurityMetadataSource</interfacename> from which
                            it obtains the metadata for a particular method or filter invocation.
                            For web security, the interceptor class is
                            <classname>FilterSecurityInterceptor</classname> and it uses the marker
                            interface
                            <interfacename>FilterInvocationSecurityMetadataSource</interfacename>.
                            The <quote>secured object</quote> type it operates on is a
                            <classname>FilterInvocation</classname>. The default implementation
                            which is used (both in the namespace <literal>&lt;http&gt;</literal> and
                            when configuring the interceptor explicitly, stores the list of URL
                            patterns and their corresponding list of <quote>configuration
                            attributes</quote> (instances of
                            <interfacename>ConfigAttribute</interfacename>) in an in-memory map. </para>
                        <para> To load the data from an alternative source, you must be using an
                            explicitly declared security filter chain (typically Spring Security's
                            <classname>FilterChainProxy</classname>) in order to customize the
                            <classname>FilterSecurityInterceptor</classname> bean. You can't use the
                            namespace. You would then implement
                            <interfacename>FilterInvocationSecurityMetadataSource</interfacename> to
                            load the data as you please for a particular
                            <classname>FilterInvocation</classname><footnote>
                            <para>The <classname>FilterInvocation</classname> object contains the
                                <classname>HttpServletRequest</classname>, so you can obtain the URL
                                or any other relevant information on which to base your decision on
                                what the list of returned attributes will contain.</para>
                            </footnote>. A very basic outline would look something like this: <programlisting language="java"><![CDATA[
  public class MyFilterSecurityMetadataSource implements FilterInvocationSecurityMetadataSource {

    public List<ConfigAttribute> getAttributes(Object object) {
      FilterInvocation fi = (FilterInvocation) object;
        String url = fi.getRequestUrl();
        String httpMethod = fi.getRequest().getMethod();
        List<ConfigAttribute> attributes = new ArrayList<ConfigAttribute>();

        // Lookup your database (or other source) using this information and populate the
        // list of attributes

        return attributes;
    }

    public Collection<ConfigAttribute> getAllConfigAttributes() {
      return null;
    }

    public boolean supports(Class<?> clazz) {
      return FilterInvocation.class.isAssignableFrom(clazz);
    }
  }
  ]]></programlisting> For more information, look at the code for
                            <classname>DefaultFilterInvocationSecurityMetadataSource</classname>.
                        </para>
                    </answer>
                </qandaentry>

                <qandaentry xml:id="faq-ldap-authorities">
                    <question>
                        <para>How do I authenticate against LDAP but load user roles from a
                            database?</para>
                    </question>
                    <answer>
                        <para> The <classname>LdapAuthenticationProvider</classname> bean (which handles
                            normal LDAP authentication in Spring Security) is configured with two
                            separate strategy interfaces, one which performs the authenticatation
                            and one which loads the user authorities, called
                            <interfacename>LdapAuthenticator</interfacename> and
                            <interfacename>LdapAuthoritiesPopulator</interfacename> respectively.
                            The <classname>DefaultLdapAuthoritiesPopulator</classname> loads the
                            user authorities from the LDAP directory and has various configuration
                            parameters to allow you to specify how these should be retrieved. </para>
                        <para> To use JDBC instead, you can implement the interface yourself, using
                            whatever SQL is appropriate for your schema: <programlisting language="java"><![CDATA[
  public class MyAuthoritiesPopulator implements LdapAuthoritiesPopulator {
    @Autowired
    JdbcTemplate template;

    List<GrantedAuthority> getGrantedAuthorities(DirContextOperations userData, String username) {
      List<GrantedAuthority> = template.query("select role from roles where username = ?",
                                                   new String[] {username},
                                                   new RowMapper<GrantedAuthority>() {
        /**
         *  We're assuming here that you're using the standard convention of using the role
         *  prefix "ROLE_" to mark attributes which are supported by Spring Security's RoleVoter.
         */
        public GrantedAuthority mapRow(ResultSet rs, int rowNum) throws SQLException {
          return new GrantedAuthorityImpl("ROLE_" + rs.getString(1);
        }
      }
    }
  }
  ]]></programlisting> You would then add a bean of this type to your application context and inject
                            it into the <code>LdapAuthenticationProvider</code>. This is covered in
                            the section on configuring LDAP using explicit Spring beans in the LDAP
                            chapter of the reference manual. Note that you can't use the namespace
                            for configuration in this case. You should also consult the Javadoc for
                            the relevant classes and interfaces. </para>
                    </answer>
                </qandaentry>
                <qandaentry xml:id="faq-namespace-post-processor">
                    <question>
                        <para>I want to modify the property of a bean that is created by the
                            namespace, but there is nothing in the schema to support it. What can I
                            do short of abandoning namespace use?</para>
                    </question>
                    <answer>
                        <para>The namespace functionality is intentionally limited, so it doesn't
                            cover everything that you can do with plain beans. If you want to do
                            something simple, like modify a bean, or inject a different dependency,
                            you can do this by adding a
                            <interfacename>BeanPostProcessor</interfacename> to your configuration.
                            More information can be found in the <link
                            xlink:href="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/htmlsingle/spring-framework-reference.html#beans-factory-extension-bpp"
                            >Spring Reference Manual</link>. In order to do this, you need to know a
                            bit about which beans are created, so you should also read the blog
                            article in the above question on <link
                            xlink:href="#faq-namespace-to-bean-mapping">how the namespace maps to
                            Spring beans</link>. </para>
                        <para> Normally, you would add the functionality you require to the
                            <methodname>postProcessBeforeInitialization</methodname> method of
                            <interfacename>BeanPostProcessor</interfacename>. Let's say that you
                            want to customize the
                            <interfacename>AuthenticationDetailsSource</interfacename> used by the
                            <classname>UsernamePasswordAuthenticationFilter</classname>, (created by
                            the <literal>form-login</literal> element). You want to extract a
                            particular header called <literal>CUSTOM_HEADER</literal>from the
                            request and make use of it while authenticating the user. The processor
                            class would look like this: <programlisting language="java"><![CDATA[
public class BeanPostProcessor implements BeanPostProcessor {

    public Object postProcessAfterInitialization(Object bean, String name) {
        if (bean instanceof UsernamePasswordAuthenticationFilter) {
            System.out.println("********* Post-processing " + name);
            ((UsernamePasswordAuthenticationFilter)bean).setAuthenticationDetailsSource(
                    new AuthenticationDetailsSource() {
                        public Object buildDetails(Object context) {
                            return ((HttpServletRequest)context).getHeader("CUSTOM_HEADER");
                        }
                    });
        }
        return bean;
    }

    public Object postProcessBeforeInitialization(Object bean, String name) {
        return bean;
    }
}
]]></programlisting> You would then register this bean in your application context. Spring will
                            automatically invoke it on the beans defined in the application context.
                        </para>
                    </answer>
                </qandaentry>

            </qandadiv>
        </qandaset>
    </section>
</article>
