spring-security/docs/faq/src/docbook/faq.xml

<?xml version="1.0" encoding="UTF-8"?>
<?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 linkend="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 changes the session ID
							when the user authenticates. If you're using a Servlet 3.1 or newer
							container, the session ID is simply changed. If you're using an older
							container, Spring Security invalidates the existing session, creates a
							new session, and transfers the session data to the new session. Changing
							the session identifier in this manner prevents
							<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. However, 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> can interfere with this because
							it results in a new session ID cookie being sent back to the user's
							browser, usually with the secure flag. To get around this, you can
							disable session fixation protection, but in newer Servlet containers
							you can also configure session cookies to never use the secure flag.
							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.web.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 linkend="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 linkend="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
							linkend="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>