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https://github.com/spring-projects/spring-security.git
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SEC-1584: Doc updates to explain request matching process.
This commit is contained in:
Luke Taylor
parent
dc1b652512
commit
161710cc87
@ -129,7 +129,11 @@
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<literal><http></literal> element is the parent for all web-related namespace
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functionality. The <literal><intercept-url></literal> element defines a
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<literal>pattern</literal> which is matched against the URLs of incoming requests using an
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ant path style syntax. The <literal>access</literal> attribute defines the access
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ant path style syntax<footnote>
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<para>See the section on <link xlink:href="#request-matching">Request
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Matching</link> in the Web Application Infrastructure chapter for more details
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on how matches are actually performed.</para>
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</footnote>. The <literal>access</literal> attribute defines the access
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requirements for requests matching the given pattern. With the default configuration, this
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is typically a comma-separated list of roles, one of which a user must have to be allowed to
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make the request. The prefix <quote>ROLE_</quote> is a marker which indicates that a simple
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@ -40,29 +40,32 @@
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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 implement
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the logic of the filter. What <classname>DelegatingFilterProxy</classname> does is delegate
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the <interfacename>Filter</interfacename>'s methods through to a bean which is obtained from
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the Spring application context. This enables the bean to benefit from the Spring web
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application context lifecycle support and configuration flexibility. The bean must implement
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<interfacename>javax.servlet.Filter</interfacename> and it must have the same name as that
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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> It should now be clear that you can declare each Spring Security filter bean that you
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require in your application context file and add a corresponding
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<classname>DelegatingFilterProxy</classname> entry to <filename>web.xml</filename> for
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each filter, making sure that they are ordered correctly. This is a cumbersome approach and
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clutters up the <filename>web.xml</filename> file quickly if we have a lot of filters. We
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would prefer to just add a single entry to <filename>web.xml</filename> and deal entirely
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with the application context file for managing our web security beans. This is where Spring
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Secuiryt's <classname>FilterChainProxy</classname> comes in. It is wired using a
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<literal>DelegatingFilterProxy</literal>, just like in the example above, but with the
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<literal>filter-name</literal> set to the bean name <quote>filterChainProxy</quote>. The
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filter chain is then declared in the application context with the same bean name. Here's an
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example: <programlisting language="xml"><![CDATA[
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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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@ -78,56 +81,175 @@
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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
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used to set 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 context
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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 the bean
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names specified in the <literal>filters</literal> element. Both regular expressions and Ant
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Paths are supported, and the most specific URIs appear first. At runtime the
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<classname>FilterChainProxy</classname> will locate the first URI pattern that matches the
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current web request and the list of filter beans specified by the <literal>filters</literal>
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attribute will be applied to that request. The filters will be invoked in the order they are
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defined, so you have complete control over the filter chain which is applied to a particular
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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 property
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of <classname>SecurityContextPersistenceFilter</classname>). As web services will never
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present a <literal>jsessionid</literal> on future requests, creating
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<literal>HttpSession</literal>s for such user agents would be wasteful. If you had a
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high-volume application which required maximum scalability, we recommend you use the
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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>In relation to lifecycle issues, the <classname>FilterChainProxy</classname> will always
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delegate <methodname>init(FilterConfig)</methodname> and <methodname>destroy()</methodname>
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methods through to the underlaying <interfacename>Filter</interfacename>s if such methods
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are called against <classname>FilterChainProxy</classname> itself. In this case,
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<classname>FilterChainProxy</classname> guarantees to only initialize and destroy each
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<literal>Filter</literal> bean once, no matter how many times it is declared in the filter
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chain(s). You control the overall choice as to whether these methods are called or not via
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the <literal>targetFilterLifecycle</literal> initialization parameter of
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<literal>DelegatingFilterProxy</literal>. By default this property is
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<literal>false</literal> and servlet container lifecycle invocations are not delegated
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through <literal>DelegatingFilterProxy</literal>.</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 the
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name of the <classname>FilterChainProxy</classname> which is created by the namespace. </para>
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<section>
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<title>Bypassing the Filter Chain</title>
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<para> As with the namespace, you can use the attribute <literal>filters = "none"</literal>
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as an alternative to supplying a filter bean list. This will omit the request pattern from
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the security filter chain entirely. Note that anything matching this path will then have
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no authentication or authorization services applied and will be freely accessible. If you
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want to make use of the contents of the <classname>SecurityContext</classname> contents
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during a request, then it must have passed through the security filter chain. Otherwise
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the <classname>SecurityContextHolder</classname> will not have been populated and the
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contents will be null.</para>
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</section>
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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>As with the namespace, 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</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. Each path segment of a URL may contain
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parameters, as defined in <link xlink:href="http://www.ietf.org/rfc/rfc2396.txt">RFC
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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> value
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and the behaviour varies between different servlet containers. There is a danger
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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. Spring Security's
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<classname>FilterChainProxy</classname> therefore wraps incoming requests to
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consistently return <literal>servletPath</literal> and <literal>pathInfo</literal>
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values which do not contain path parameters. 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>. It is therefore essential that a
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<classname>FilterChainProxy</classname> is used to manage the security filter
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chain.</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. Matching is performed
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a pattern against the concatenated <literal>servletPath</literal> and
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<literal>pathInfo</literal>, ignoring the <literal>queryString</literal>, and is case insensitive by default.</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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<section>
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<title>Filter Ordering</title>
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