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-<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="web-infrastructure"
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- xmlns:xlink="http://www.w3.org/1999/xlink">
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- <info>
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- <title>Web Application Infrastructure</title>
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- </info>
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-
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- <section xml:id="filters">
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- <title>The Security Filter Chain</title>
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- <para>Spring Security's web infrastructure is based entirely on standard servlet filters. It
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- doesn't use servlets or any other servlet-based frameworks (such as Spring MVC)
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- internally, so it has no strong links to any particular web technology. It deals in
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- <classname>HttpServletRequest</classname>s and
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- <classname>HttpServletResponse</classname>s and doesn't care whether the requests come
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- from a browser, a web service client, an <classname>HttpInvoker</classname> or an AJAX
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- application. </para>
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- <para> Spring Security maintains a filter chain internally where each of the filters has a
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- particular responsibility and filters are added or removed from the configuration
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- depending on which services are required. The ordering of the filters is important as
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- there are dependencies between them. If you have been using <link
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- xlink:href="#ns-config">namespace configuration</link>, then the filters are
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- automatically configured for you and you don't have to define any Spring beans
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- explicitly but here may be times when you want full control over the security filter
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- chain, either because you are using features which aren't supported in the namespace, or
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- you are using your own customized versions of classes.</para>
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- <section xml:id="delegating-filter-proxy">
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- <title><classname>DelegatingFilterProxy</classname></title>
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- <para> When using servlet filters, you obviously need to declare them in your
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- <filename>web.xml</filename>, or they will be ignored by the servlet container. In
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- Spring Security, the filter classes are also Spring beans defined in the application
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- context and thus able to take advantage of Spring's rich dependency-injection
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- facilities and lifecycle interfaces. Spring's
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- <classname>DelegatingFilterProxy</classname> provides the link between
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- <filename>web.xml</filename> and the application context. </para>
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- <para>When using <classname>DelegatingFilterProxy</classname>, you will see something
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- like this in the <filename>web.xml</filename> file: <programlisting><![CDATA[
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- <filter>
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- <filter-name>myFilter</filter-name>
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- <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
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- </filter>
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-
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- <filter-mapping>
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- <filter-name>myFilter</filter-name>
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- <url-pattern>/*</url-pattern>
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- </filter-mapping>]]>
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- </programlisting> Notice that the filter is actually a
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- <literal>DelegatingFilterProxy</literal>, and not the class that will actually
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- implement the logic of the filter. What <classname>DelegatingFilterProxy</classname>
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- does is delegate the <interfacename>Filter</interfacename>'s methods through to a
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- bean which is obtained from the Spring application context. This enables the bean to
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- benefit from the Spring web application context lifecycle support and configuration
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- flexibility. The bean must implement
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- <interfacename>javax.servlet.Filter</interfacename> and it must have the same name
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- as that in the <literal>filter-name</literal> element. Read the Javadoc for
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- <classname>DelegatingFilterProxy</classname> for more information</para>
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- </section>
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- <section xml:id="filter-chain-proxy">
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- <title><classname>FilterChainProxy</classname></title>
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- <para>Spring Security's web infrastructure should only be used by delegating to an
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- instance of <classname>FilterChainProxy</classname>. The security filters should not
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- be used by themselves In theory you could declare each Spring Security filter bean
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- that you require in your application context file and add a corresponding
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- <classname>DelegatingFilterProxy</classname> entry to <filename>web.xml</filename>
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- for each filter, making sure that they are ordered correctly, but this would be
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- cumbersome and would clutter up the <filename>web.xml</filename> file quickly if you
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- have a lot of filters. <classname>FilterChainProxy</classname> lets us add a single
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- entry to <filename>web.xml</filename> and deal entirely with the application context
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- file for managing our web security beans. It is wired using a
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- <literal>DelegatingFilterProxy</literal>, just like in the example above, but with
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- the <literal>filter-name</literal> set to the bean name
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- <quote>filterChainProxy</quote>. The filter chain is then declared in the
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- application context with the same bean name. Here's an example: <programlisting language="xml"><![CDATA[
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-<bean id="filterChainProxy" class="org.springframework.security.web.FilterChainProxy">
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- <sec:filter-chain-map path-type="ant">
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- <sec:filter-chain pattern="/webServices/**" filters="
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- securityContextPersistenceFilterWithASCFalse,
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- basicProcessingFilter,
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- exceptionTranslationFilter,
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- filterSecurityInterceptor" />
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- <sec:filter-chain pattern="/**" filters="
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- securityContextPersistenceFilterWithASCTrue,
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- authenticationProcessingFilter,
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- exceptionTranslationFilter,
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- filterSecurityInterceptor" />
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- </sec:filter-chain-map>
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-</bean>
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-]]>
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- </programlisting> The namespace element <literal>filter-chain-map</literal> is used to set
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- up the security filter chain(s) which are required within the application<footnote>
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- <para>Note that you'll need to include the security namespace in your application
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- context XML file in order to use this syntax.</para>
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- </footnote>. It maps a particular URL pattern to a chain of filters built up from
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- the bean names specified in the <literal>filters</literal> element. Both regular
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- expressions and Ant Paths are supported, and the most specific URLs appear first. At
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- runtime the <classname>FilterChainProxy</classname> will locate the first URL
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- pattern that matches the current web request and the list of filter beans specified
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- by the <literal>filters</literal> attribute will be applied to that request. The
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- filters will be invoked in the order they are defined, so you have complete control
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- over the filter chain which is applied to a particular URL.</para>
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- <para>You may have noticed we have declared two
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- <classname>SecurityContextPersistenceFilter</classname>s in the filter chain
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- (<literal>ASC</literal> is short for <literal>allowSessionCreation</literal>, a
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- property of <classname>SecurityContextPersistenceFilter</classname>). As web
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- services will never present a <literal>jsessionid</literal> on future requests,
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- creating <literal>HttpSession</literal>s for such user agents would be wasteful. If
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- you had a high-volume application which required maximum scalability, we recommend
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- you use the approach shown above. For smaller applications, using a single
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- <classname>SecurityContextPersistenceFilter</classname> (with its default
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- <literal>allowSessionCreation</literal> as <literal>true</literal>) would likely be
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- sufficient.</para>
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- <para>Note that <classname>FilterChainProxy</classname> does not invoke standard filter
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- lifecycle methods on the filters it is configured with. We recommend you use
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- Spring's application context lifecycle interfaces as an alternative, just as you
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- would for any other Spring bean.</para>
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- <para> When we looked at how to set up web security using <link
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- xlink:href="#namespace-auto-config">namespace configuration</link>, we used a
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- <literal>DelegatingFilterProxy</literal> with the name
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- <quote>springSecurityFilterChain</quote>. You should now be able to see that this is
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- the name of the <classname>FilterChainProxy</classname> which is created by the
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- namespace. </para>
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- <section>
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- <title>Bypassing the Filter Chain</title>
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- <para> You can use the attribute <literal>filters = "none"</literal> as an
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- alternative to supplying a filter bean list. This will omit the request pattern
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- from the security filter chain entirely. Note that anything matching this path
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- will then have no authentication or authorization services applied and will be
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- freely accessible. If you want to make use of the contents of the
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- <classname>SecurityContext</classname> contents during a request, then it must
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- have passed through the security filter chain. Otherwise the
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- <classname>SecurityContextHolder</classname> will not have been populated and
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- the contents will be null.</para>
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- </section>
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- </section>
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- <section>
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- <title>Filter Ordering</title>
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- <para>The order that filters are defined in the chain is very important. Irrespective of
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- which filters you are actually using, the order should be as follows: <orderedlist>
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- <listitem>
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- <para><classname>ChannelProcessingFilter</classname>, because it might need to
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- redirect to a different protocol</para>
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- </listitem>
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- <listitem>
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- <para><classname>ConcurrentSessionFilter</classname>, because it doesn't use any
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- <classname>SecurityContextHolder</classname> functionality but needs to
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- update the <interfacename>SessionRegistry</interfacename> to reflect ongoing
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- requests from the principal</para>
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- </listitem>
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- <listitem>
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- <para><classname>SecurityContextPersistenceFilter</classname>, so a
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- <interfacename>SecurityContext</interfacename> can be set up in the
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- <classname>SecurityContextHolder</classname> at the beginning of a web
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- request, and any changes to the
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- <interfacename>SecurityContext</interfacename> can be copied to the
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- <literal>HttpSession</literal> when the web request ends (ready for use with
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- the next web request)</para>
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- </listitem>
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- <listitem>
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- <para>Authentication processing mechanisms -
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- <classname>UsernamePasswordAuthenticationFilter</classname>,
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- <classname>CasProcessingFilter</classname>,
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- <classname>BasicProcessingFilter</classname> etc - so that the
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- <classname>SecurityContextHolder</classname> can be modified to contain a
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- valid <interfacename>Authentication</interfacename> request token</para>
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- </listitem>
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- <listitem>
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- <para>The <literal>SecurityContextHolderAwareRequestFilter</literal>, if you are
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- using it to install a Spring Security aware
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- <literal>HttpServletRequestWrapper</literal> into your servlet
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- container</para>
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- </listitem>
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- <listitem>
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- <para><classname>RememberMeProcessingFilter</classname>, so that if no earlier
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- authentication processing mechanism updated the
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- <classname>SecurityContextHolder</classname>, and the request presents a
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- cookie that enables remember-me services to take place, a suitable
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- remembered <interfacename>Authentication</interfacename> object will be put
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- there</para>
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- </listitem>
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- <listitem>
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- <para><classname>AnonymousProcessingFilter</classname>, so that if no earlier
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- authentication processing mechanism updated the
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- <classname>SecurityContextHolder</classname>, an anonymous
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- <interfacename>Authentication</interfacename> object will be put
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- there</para>
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- </listitem>
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- <listitem>
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- <para><classname>ExceptionTranslationFilter</classname>, to catch any Spring
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- Security exceptions so that either an HTTP error response can be returned or
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- an appropriate <interfacename>AuthenticationEntryPoint</interfacename> can
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- be launched</para>
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- </listitem>
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- <listitem>
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- <para><classname>FilterSecurityInterceptor</classname>, to protect web URIs and
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- raise exceptions when access is denied</para>
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- </listitem>
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- </orderedlist></para>
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- </section>
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- <section xml:id="request-matching">
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- <title>Request Matching and <interfacename>HttpFirewall</interfacename></title>
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- <para>Spring Security has several areas where patterns you have defined are tested
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- against incoming requests in order to decide how the request should be handled. This
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- occurs when the <classname>FilterChainProxy</classname> decides which filter chain a
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- request should be passed through and also when the
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- <classname>FilterSecurityInterceptor</classname> decides which security constraints
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- apply to a request. It's important to understand what the mechanism is and what URL
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- value is used when testing against the patterns that you define.</para>
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- <para>The Servlet Specification defines several properties for the
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- <interfacename>HttpServletRequest</interfacename> which are accessible via getter
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- methods, and which we might want to match against. These are the
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- <literal>contextPath</literal>, <literal>servletPath</literal>,
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- <literal>pathInfo</literal> and <literal>queryString</literal>. Spring Security is
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- only interested in securing paths within the application, so the
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- <literal>contextPath</literal> is ignored. Unfortunately, the servlet spec does not
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- define exactly what the values of <literal>servletPath</literal> and
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- <literal>pathInfo</literal> will contain for a particular request URI. For example,
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- each path segment of a URL may contain parameters, as defined in <link
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- xlink:href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</link><footnote>
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- <para>You have probably seen this when a browser doesn't support cookies and the
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- <literal>jsessionid</literal> parameter is appended to the URL after a
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- semi-colon. However the RFC allows the presence of these parameters in any path
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- segment of the URL</para>
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- </footnote>. The Specification does not clearly state whether these should be
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- included in the <literal>servletPath</literal> and <literal>pathInfo</literal>
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- values and the behaviour varies between different servlet containers. There is a
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- danger that when an application is deployed in a container which does not strip path
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- parameters from these values, an attacker could add them to the requested URL in
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- order to cause a pattern match to succeed or fail unexpectedly.<footnote>
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- <para>The original values will be returned once the request leaves the
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- <classname>FilterChainProxy</classname>, so will still be available to the
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- application.</para>
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- </footnote>. Other variations in the incoming URL are also possible. For example, it
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- could contain path-traversal sequences (like <literal>/../</literal>) or multiple
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- forward slashes (<literal>//</literal>) which could also cause pattern-matches to
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- fail. Some containers normalize these out before performing the servlet mapping, but
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- others don't. To protect against issues like these,
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- <classname>FilterChainProxy</classname> uses an
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- <interfacename>HttpFirewall</interfacename> strategy to check and wrap the request.
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- Un-normalized requests are automatically rejected by default, and path parameters
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- and duplicate slashes are removed for matching purposes.<footnote>
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- <para>So, for example, an original request path
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- <literal>/secure;hack=1/somefile.html;hack=2</literal> will be returned as
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- <literal>/secure/somefile.html</literal>.</para>
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- </footnote>. It is therefore essential that a
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- <classname>FilterChainProxy</classname> is used to manage the security filter chain.
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- Note that the <literal>servletPath</literal> and <literal>pathInfo</literal> values
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- are decoded by the container, so your application should not have any valid paths
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- which contain semi-colons, as these parts will be removed for matching purposes. </para>
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- <para>As mentioned above, the default strategy is to use Ant-style paths for matching
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- and this is likely to be the best choice for most users. The strategy is implemented
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- in the class <classname>AntPathRequestMatcher</classname> which uses Spring's
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- <classname>AntPathMatcher</classname> to perform a case-insensitive match of the
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- pattern against the concatenated <literal>servletPath</literal> and
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- <literal>pathInfo</literal>, ignoring the <literal>queryString</literal>.</para>
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- <para>If for some reason, you need a more powerful matching strategy, you can use
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- regular expressions. The strategy implementation is then
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- <classname>RegexRequestMatcher</classname>. See the Javadoc for this class for more
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- information.</para>
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- <para>In practice we recommend that you use method security at your service layer, to
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- control access to your application, and do not rely entirely on the use of security
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- constraints defined at the web-application level. URLs change and it is difficult to
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- take account of all the possible URLs that an application might support and how
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- requests might be manipulated. You should try and restrict yourself to using a few
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- simple ant paths which are simple to understand. Always try to use a
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- <quote>deny-by-default</quote> approach where you have a catch-all wildcard
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- (<literal>/**</literal>) defined last and denying access.</para>
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- <para>Security defined at the service layer is much more robust and harder to bypass, so
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- you should always take advantage of Spring Security's method security
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- options.</para>
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- </section>
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- <section>
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- <title>Use with other Filter-Based Frameworks</title>
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- <para>If you're using some other framework that is also filter-based, then you need to
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- make sure that the Spring Security filters come first. This enables the
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- <classname>SecurityContextHolder</classname> to be populated in time for use by the
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- other filters. Examples are the use of SiteMesh to decorate your web pages or a web
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- framework like Wicket which uses a filter to handle its requests. </para>
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- </section>
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- </section>
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- <!--
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- <section xml:id="taglib">
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- <info>
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- <title>Tag Libraries</title>
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- </info>
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- <para>Spring Security comes bundled with several JSP tag libraries which provide a range of
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- different services.</para>
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- <section xml:id="taglib-config">
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- <info>
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- <title>Configuration</title>
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- </info>
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- <para>All taglib classes are included in the core
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- <literal>spring-security-taglibs-<version>.jar</literal> file, with the
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- <literal>security.tld</literal> located in the JAR's <literal>META-INF</literal>
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- directory. This means for JSP 1.2+ web containers you can simply include the JAR in the
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- WAR's <literal>WEB-INF/lib</literal> directory and it will be available.</para>
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- </section>
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- <section xml:id="taglib-usage">
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- <info>
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- <title>Usage</title>
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- </info>
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- <para>Now that you've configured the tag libraries, refer to the individual reference guide
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- sections for details on how to use them. Note that when using the tags, you should include
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- the taglib reference in your JSP:
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- <programlisting>
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- <%@ taglib prefix='security' uri='http://www.springframework.org/security/tags' %>
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-</programlisting></para>
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- </section>
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- </section>
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-
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-<section xml:id="authentication-taglibs">
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-<info>
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-<title>Authentication Tag Libraries</title>
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-</info>
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-<para><literal>AuthenticationTag</literal> is used to simply output a property of the current
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-<interfacename>Authentication</interfacename> object to the web page.</para>
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-<para>The following JSP fragment illustrates how to use the
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-<literal>AuthenticationTag</literal>:</para>
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-<para>
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-<programlisting><security:authentication property="principal.username"/></programlisting>
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-</para>
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-<para>This tag would cause the principal's name to be output. Here we are assuming the
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-<literal>Authentication.getPrincipal()</literal> is a
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-<interfacename>UserDetails</interfacename> object, which is generally the case when using
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-one of Spring Security's stadard <classname>AuthenticationProvider</classname>
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-implementations.</para>
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-</section>
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-
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-
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-
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--->
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-</chapter>
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Luke Taylor