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