329 lines
16 KiB
Plaintext
329 lines
16 KiB
Plaintext
[[servlet-architecture]]
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= Architecture
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:figures: servlet/architecture
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This section discusses Spring Security's high-level architecture within Servlet based applications.
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We build on this high-level understanding within the xref:servlet/authentication/index.adoc#servlet-authentication[Authentication], xref:servlet/authorization/index.adoc#servlet-authorization[Authorization], and xref:servlet/exploits/index.adoc#servlet-exploits[Protection Against Exploits] sections of the reference.
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// FIXME: Add links to other sections of architecture
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[[servlet-filters-review]]
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== A Review of Filters
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Spring Security's Servlet support is based on Servlet Filters, so it is helpful to look at the role of Filters generally first.
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The following image shows the typical layering of the handlers for a single HTTP request.
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.FilterChain
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[[servlet-filterchain-figure]]
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image::{figures}/filterchain.png[]
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The client sends a request to the application, and the container creates a `FilterChain`, which contains the `Filter` instances and `Servlet` that should process the `HttpServletRequest`, based on the path of the request URI.
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In a Spring MVC application, the `Servlet` is an instance of {spring-framework-reference-url}web.html#mvc-servlet[`DispatcherServlet`].
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At most, one `Servlet` can handle a single `HttpServletRequest` and `HttpServletResponse`.
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However, more than one `Filter` can be used to:
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* Prevent downstream `Filter` instances or the `Servlet` from being invoked.
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In this case, the `Filter` typically writes the `HttpServletResponse`.
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* Modify the `HttpServletRequest` or `HttpServletResponse` used by the downstream `Filter` instances and the `Servlet`.
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The power of the `Filter` comes from the `FilterChain` that is passed into it.
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.`FilterChain` Usage Example
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====
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.Java
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[source,java,role="primary"]
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----
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public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
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// do something before the rest of the application
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chain.doFilter(request, response); // invoke the rest of the application
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// do something after the rest of the application
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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fun doFilter(request: ServletRequest, response: ServletResponse, chain: FilterChain) {
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// do something before the rest of the application
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chain.doFilter(request, response) // invoke the rest of the application
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// do something after the rest of the application
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}
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----
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====
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Since a `Filter` impacts only downstream `Filter` instances and the `Servlet`, the order in which each `Filter` is invoked is extremely important.
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[[servlet-delegatingfilterproxy]]
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== DelegatingFilterProxy
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Spring provides a `Filter` implementation named {spring-framework-api-url}org/springframework/web/filter/DelegatingFilterProxy.html[`DelegatingFilterProxy`] that allows bridging between the Servlet container's lifecycle and Spring's `ApplicationContext`.
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The Servlet container allows registering `Filter` instances by using its own standards, but it is not aware of Spring-defined Beans.
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You can register `DelegatingFilterProxy` through the standard Servlet container mechanisms but delegate all the work to a Spring Bean that implements `Filter`.
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Here is a picture of how `DelegatingFilterProxy` fits into the <<servlet-filters-review,`Filter` instances and the `FilterChain`>>.
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.DelegatingFilterProxy
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[[servlet-delegatingfilterproxy-figure]]
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image::{figures}/delegatingfilterproxy.png[]
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`DelegatingFilterProxy` looks up __Bean Filter~0~__ from the `ApplicationContext` and then invokes __Bean Filter~0~__.
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The following listing shows pseudo code of `DelegatingFilterProxy`:
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.`DelegatingFilterProxy` Pseudo Code
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====
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.Java
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[source,java,role="primary"]
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----
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public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
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Filter delegate = getFilterBean(someBeanName); // <1>
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delegate.doFilter(request, response); // <2>
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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fun doFilter(request: ServletRequest, response: ServletResponse, chain: FilterChain) {
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val delegate: Filter = getFilterBean(someBeanName) // <1>
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delegate.doFilter(request, response) // <2>
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}
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----
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====
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<1> Lazily get Filter that was registered as a Spring Bean.
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For the example in <<servlet-delegatingfilterproxy-figure>> `delegate` is an instance of __Bean Filter~0~__.
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<2> Delegate work to the Spring Bean.
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Another benefit of `DelegatingFilterProxy` is that it allows delaying looking up `Filter` bean instances.
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This is important because the container needs to register the `Filter` instances before the container can start up.
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However, Spring typically uses a `ContextLoaderListener` to load the Spring Beans, which is not done until after the `Filter` instances need to be registered.
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[[servlet-filterchainproxy]]
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== FilterChainProxy
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Spring Security's Servlet support is contained within `FilterChainProxy`.
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`FilterChainProxy` is a special `Filter` provided by Spring Security that allows delegating to many `Filter` instances through <<servlet-securityfilterchain,`SecurityFilterChain`>>.
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Since `FilterChainProxy` is a Bean, it is typically wrapped in a <<servlet-delegatingfilterproxy>>.
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The following image shows the role of `FilterChainProxy`.
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.FilterChainProxy
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[[servlet-filterchainproxy-figure]]
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image::{figures}/filterchainproxy.png[]
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[[servlet-securityfilterchain]]
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== SecurityFilterChain
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{security-api-url}org/springframework/security/web/SecurityFilterChain.html[`SecurityFilterChain`] is used by <<servlet-filterchainproxy>> to determine which Spring Security `Filter` instances should be invoked for the current request.
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The following image shows the role of `SecurityFilterChain`.
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.SecurityFilterChain
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[[servlet-securityfilterchain-figure]]
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image::{figures}/securityfilterchain.png[]
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The <<servlet-security-filters,Security Filters>> in `SecurityFilterChain` are typically Beans, but they are registered with `FilterChainProxy` instead of <<servlet-delegatingfilterproxy>>.
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`FilterChainProxy` provides a number of advantages to registering directly with the Servlet container or <<servlet-delegatingfilterproxy>>.
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First, it provides a starting point for all of Spring Security's Servlet support.
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For that reason, if you try to troubleshoot Spring Security's Servlet support, adding a debug point in `FilterChainProxy` is a great place to start.
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Second, since `FilterChainProxy` is central to Spring Security usage, it can perform tasks that are not viewed as optional.
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// FIXME: Add a link to SecurityContext
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For example, it clears out the `SecurityContext` to avoid memory leaks.
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It also applies Spring Security's xref:servlet/exploits/firewall.adoc#servlet-httpfirewall[`HttpFirewall`] to protect applications against certain types of attacks.
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In addition, it provides more flexibility in determining when a `SecurityFilterChain` should be invoked.
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In a Servlet container, `Filter` instances are invoked based upon the URL alone.
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// FIXME: Link to RequestMatcher
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However, `FilterChainProxy` can determine invocation based upon anything in the `HttpServletRequest` by using the `RequestMatcher` interface.
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The following image shows multiple `SecurityFilterChain` instances:
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.Multiple SecurityFilterChain
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[[servlet-multi-securityfilterchain-figure]]
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image::{figures}/multi-securityfilterchain.png[]
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In the <<servlet-multi-securityfilterchain-figure>> figure, `FilterChainProxy` decides which `SecurityFilterChain` should be used.
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Only the first `SecurityFilterChain` that matches is invoked.
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If a URL of `/api/messages/` is requested, it first matches on the `SecurityFilterChain~0~` pattern of `+/api/**+`, so only `SecurityFilterChain~0~` is invoked, even though it also matches on ``SecurityFilterChain~n~``.
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If a URL of `/messages/` is requested, it does not match on the `SecurityFilterChain~0~` pattern of `+/api/**+`, so `FilterChainProxy` continues trying each `SecurityFilterChain`.
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Assuming that no other `SecurityFilterChain` instances match, `SecurityFilterChain~n~` is invoked.
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// FIXME: add link to pattern matching
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Notice that `SecurityFilterChain~0~` has only three security `Filter` instances configured.
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However, `SecurityFilterChain~n~` has four security `Filter` instanes configured.
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It is important to note that each `SecurityFilterChain` can be unique and can be configured in isolation.
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In fact, a `SecurityFilterChain` might have zero security `Filter` instances if the application wants Spring Security to ignore certain requests.
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// FIXME: add link to configuring multiple `SecurityFilterChain` instances
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[[servlet-security-filters]]
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== Security Filters
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The Security Filters are inserted into the <<servlet-filterchainproxy>> with the <<servlet-securityfilterchain>> API.
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The <<servlet-filters-review,order of `Filter`>> instances matters.
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It is typically not necessary to know the ordering of Spring Security's `Filter` instances.
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However, there are times that it is beneficial to know the ordering.
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The following is a comprehensive list of Spring Security Filter ordering:
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* xref:servlet/authentication/session-management.adoc#session-mgmt-force-session-creation[`ForceEagerSessionCreationFilter`]
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* `ChannelProcessingFilter`
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* `WebAsyncManagerIntegrationFilter`
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* `SecurityContextPersistenceFilter`
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* `HeaderWriterFilter`
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* `CorsFilter`
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* `CsrfFilter`
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* `LogoutFilter`
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* `OAuth2AuthorizationRequestRedirectFilter`
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* `Saml2WebSsoAuthenticationRequestFilter`
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* `X509AuthenticationFilter`
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* `AbstractPreAuthenticatedProcessingFilter`
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* `CasAuthenticationFilter`
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* `OAuth2LoginAuthenticationFilter`
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* `Saml2WebSsoAuthenticationFilter`
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* xref:servlet/authentication/passwords/form.adoc#servlet-authentication-usernamepasswordauthenticationfilter[`UsernamePasswordAuthenticationFilter`]
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* `DefaultLoginPageGeneratingFilter`
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* `DefaultLogoutPageGeneratingFilter`
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* `ConcurrentSessionFilter`
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* xref:servlet/authentication/passwords/digest.adoc#servlet-authentication-digest[`DigestAuthenticationFilter`]
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* `BearerTokenAuthenticationFilter`
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* xref:servlet/authentication/passwords/basic.adoc#servlet-authentication-basic[`BasicAuthenticationFilter`]
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* <<requestcacheawarefilter,RequestCacheAwareFilter>>
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* `SecurityContextHolderAwareRequestFilter`
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* `JaasApiIntegrationFilter`
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* `RememberMeAuthenticationFilter`
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* `AnonymousAuthenticationFilter`
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* `OAuth2AuthorizationCodeGrantFilter`
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* `SessionManagementFilter`
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* <<servlet-exceptiontranslationfilter,`ExceptionTranslationFilter`>>
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* xref:servlet/authorization/authorize-requests.adoc#servlet-authorization-filtersecurityinterceptor[`FilterSecurityInterceptor`]
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* `SwitchUserFilter`
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[[servlet-exceptiontranslationfilter]]
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== Handling Security Exceptions
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The {security-api-url}org/springframework/security/web/access/ExceptionTranslationFilter.html[`ExceptionTranslationFilter`] allows translation of {security-api-url}org/springframework/security/access/AccessDeniedException.html[`AccessDeniedException`] and {security-api-url}/org/springframework/security/core/AuthenticationException.html[`AuthenticationException`] into HTTP responses.
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`ExceptionTranslationFilter` is inserted into the <<servlet-filterchainproxy>> as one of the <<servlet-security-filters>>.
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The following image shows the relationship of `ExceptionTranslationFilter` to other components:
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image::{figures}/exceptiontranslationfilter.png[]
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* image:{icondir}/number_1.png[] First, the `ExceptionTranslationFilter` invokes `FilterChain.doFilter(request, response)` to invoke the rest of the application.
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* image:{icondir}/number_2.png[] If the user is not authenticated or it is an `AuthenticationException`, then __Start Authentication__.
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** The xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontextholder[SecurityContextHolder] is cleared out.
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** The `HttpServletRequest` is <<savedrequests,saved>> so that it can be used to replay the original request once authentication is successful.
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// FIXME: add link to authentication success
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** The `AuthenticationEntryPoint` is used to request credentials from the client.
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For example, it might redirect to a log in page or send a `WWW-Authenticate` header.
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// FIXME: link to AuthenticationEntryPoint
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* image:{icondir}/number_3.png[] Otherwise, if it is an `AccessDeniedException`, then __Access Denied__.
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The `AccessDeniedHandler` is invoked to handle access denied.
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// FIXME: link to AccessDeniedHandler
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[NOTE]
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====
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If the application does not throw an `AccessDeniedException` or an `AuthenticationException`, then `ExceptionTranslationFilter` does not do anything.
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====
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The pseudocode for `ExceptionTranslationFilter` looks something like this:
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====
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.ExceptionTranslationFilter pseudocode
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[source,java]
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----
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try {
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filterChain.doFilter(request, response); // <1>
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} catch (AccessDeniedException | AuthenticationException ex) {
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if (!authenticated || ex instanceof AuthenticationException) {
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startAuthentication(); // <2>
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} else {
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accessDenied(); // <3>
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}
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}
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----
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<1> As described in <<servlet-filters-review>>, invoking `FilterChain.doFilter(request, response)` is the equivalent of invoking the rest of the application.
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This means that if another part of the application, (<<servlet-authorization-filtersecurityinterceptor,`FilterSecurityInterceptor`>> or method security) throws an `AuthenticationException` or `AccessDeniedException` it is caught and handled here.
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<2> If the user is not authenticated or it is an `AuthenticationException`, __Start Authentication__.
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<3> Otherwise, __Access Denied__
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====
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[[savedrequests]]
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== Saving Requests Between Authentication
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As illustrated in <<servlet-exceptiontranslationfilter>>, when a request has no authentication and is for a resource that requires authentication, there is a need to save the request for the authenticated resource to re-request after authentication is successful.
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In Spring Security this is done by saving the `HttpServletRequest` using a <<requestcache,`RequestCache`>> implementation.
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[[requestcache]]
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=== RequestCache
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The `HttpServletRequest` is saved in the {security-api-url}org/springframework/security/web/savedrequest/RequestCache.html[`RequestCache`].
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When the user successfully authenticates, the `RequestCache` is used to replay the original request.
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The <<requestcacheawarefilter,`RequestCacheAwareFilter`>> is what uses the `RequestCache` to save the `HttpServletRequest`.
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By default, an `HttpSessionRequestCache` is used.
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The code below demonstrates how to customize the `RequestCache` implementation that is used to check the `HttpSession` for a saved request if the parameter named `continue` is present.
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include::partial$servlet/architecture/request-cache-continue.adoc[]
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[[requestcache-prevent-saved-request]]
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==== Prevent the Request From Being Saved
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There are a number of reasons you may want to not store the user's unauthenticated request in the session.
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You may want to offload that storage onto the user's browser or store it in a database.
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Or you may want to shut off this feature since you always want to redirect the user to the home page instead of the page they tried to visit before login.
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To do that, you can use {security-api-url}org/springframework/security/web/savedrequest/NullRequestCache.html[the `NullRequestCache` implementation].
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.Prevent the Request From Being Saved
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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SecurityFilterChain springSecurity(HttpSecurity http) throws Exception {
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RequestCache nullRequestCache = new NullRequestCache();
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http
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// ...
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.requestCache((cache) -> cache
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.requestCache(nullRequestCache)
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);
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return http.build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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open fun springSecurity(http: HttpSecurity): SecurityFilterChain {
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val nullRequestCache = NullRequestCache()
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http {
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requestCache {
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requestCache = nullRequestCache
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}
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}
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return http.build()
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}
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----
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.XML
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[source,xml,role="secondary"]
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----
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<http auto-config="true">
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<!-- ... -->
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<request-cache ref="nullRequestCache"/>
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</http>
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<b:bean id="nullRequestCache" class="org.springframework.security.web.savedrequest.NullRequestCache"/>
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----
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====
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[[requestcacheawarefilter]]
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=== RequestCacheAwareFilter
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The {security-api-url}org/springframework/security/web/savedrequest/RequestCacheAwareFilter.html[`RequestCacheAwareFilter`] uses the <<requestcache,`RequestCache`>> to save the `HttpServletRequest`.
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