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Servlet Authentication Architecture
This discussion expands on Servlet Security: The Big Picture to describe the main architectural components of Spring Security’s used in Servlet authentication. If you need concrete flows that explain how these pieces fit together, look at the Authentication Mechanism specific sections.
-
SecurityContextHolder - The
SecurityContextHolder
is where Spring Security stores the details of who is authenticated. -
SecurityContext - is obtained from the
SecurityContextHolder
and contains theAuthentication
of the currently authenticated user. -
Authentication - Can be the input to
AuthenticationManager
to provide the credentials a user has provided to authenticate or the current user from theSecurityContext
. -
GrantedAuthority - An authority that is granted to the principal on the
Authentication
(i.e. roles, scopes, etc.) -
AuthenticationManager - the API that defines how Spring Security’s Filters perform authentication.
-
ProviderManager - the most common implementation of
AuthenticationManager
. -
AuthenticationProvider - used by
ProviderManager
to perform a specific type of authentication. -
Request Credentials with
AuthenticationEntryPoint
- used for requesting credentials from a client (i.e. redirecting to a log in page, sending aWWW-Authenticate
response, etc.) -
AbstractAuthenticationProcessingFilter - a base
Filter
used for authentication. This also gives a good idea of the high level flow of authentication and how pieces work together.
SecurityContextHolder
At the heart of Spring Security’s authentication model is the SecurityContextHolder
.
It contains the SecurityContext.
![securitycontextholder](../../_images/servlet/authentication/architecture/securitycontextholder.png)
The SecurityContextHolder
is where Spring Security stores the details of who is authenticated.
Spring Security does not care how the SecurityContextHolder
is populated.
If it contains a value, then it is used as the currently authenticated user.
The simplest way to indicate a user is authenticated is to set the SecurityContextHolder
directly.
SecurityContextHolder
-
Java
-
Kotlin
SecurityContext context = SecurityContextHolder.createEmptyContext(); (1)
Authentication authentication =
new TestingAuthenticationToken("username", "password", "ROLE_USER"); (2)
context.setAuthentication(authentication);
SecurityContextHolder.setContext(context); (3)
val context: SecurityContext = SecurityContextHolder.createEmptyContext() (1)
val authentication: Authentication = TestingAuthenticationToken("username", "password", "ROLE_USER") (2)
context.authentication = authentication
SecurityContextHolder.setContext(context) (3)
1 | We start by creating an empty SecurityContext .
It is important to create a new SecurityContext instance instead of using SecurityContextHolder.getContext().setAuthentication(authentication) to avoid race conditions across multiple threads. |
2 | Next we create a new Authentication object.
Spring Security does not care what type of Authentication implementation is set on the SecurityContext .
Here we use TestingAuthenticationToken because it is very simple.
A more common production scenario is UsernamePasswordAuthenticationToken(userDetails, password, authorities) . |
3 | Finally, we set the SecurityContext on the SecurityContextHolder .
Spring Security will use this information for authorization. |
If you wish to obtain information about the authenticated principal, you can do so by accessing the SecurityContextHolder
.
-
Java
-
Kotlin
SecurityContext context = SecurityContextHolder.getContext();
Authentication authentication = context.getAuthentication();
String username = authentication.getName();
Object principal = authentication.getPrincipal();
Collection<? extends GrantedAuthority> authorities = authentication.getAuthorities();
val context = SecurityContextHolder.getContext()
val authentication = context.authentication
val username = authentication.name
val principal = authentication.principal
val authorities = authentication.authorities
By default the SecurityContextHolder
uses a ThreadLocal
to store these details, which means that the SecurityContext
is always available to methods in the same thread, even if the SecurityContext
is not explicitly passed around as an argument to those methods.
Using a ThreadLocal
in this way is quite safe if care is taken to clear the thread after the present principal’s request is processed.
Spring Security’s FilterChainProxy ensures that the SecurityContext
is always cleared.
Some applications aren’t entirely suitable for using a ThreadLocal
, because of the specific way they work with threads.
For example, a Swing client might want all threads in a Java Virtual Machine to use the same security context.
SecurityContextHolder
can be configured with a strategy on startup to specify how you would like the context to be stored.
For a standalone application you would use the SecurityContextHolder.MODE_GLOBAL
strategy.
Other applications might want to have threads spawned by the secure thread also assume the same security identity.
This is achieved by using SecurityContextHolder.MODE_INHERITABLETHREADLOCAL
.
You can change the mode from the default SecurityContextHolder.MODE_THREADLOCAL
in two ways.
The first is to set a system property, the second is to call a static method on SecurityContextHolder
.
Most applications won’t need to change from the default, but if you do, take a look at the Javadoc for SecurityContextHolder
to learn more.
SecurityContext
The SecurityContext
is obtained from the SecurityContextHolder.
The SecurityContext
contains an Authentication object.
Authentication
The Authentication
serves two main purposes within Spring Security:
-
An input to
AuthenticationManager
to provide the credentials a user has provided to authenticate. When used in this scenario,isAuthenticated()
returnsfalse
. -
Represents the currently authenticated user. The current
Authentication
can be obtained from the SecurityContext.
The Authentication
contains:
-
principal
- identifies the user. When authenticating with a username/password this is often an instance ofUserDetails
. -
credentials
- often a password. In many cases this will be cleared after the user is authenticated to ensure it is not leaked. -
authorities
- theGrantedAuthority
s are high level permissions the user is granted. A few examples are roles or scopes.
GrantedAuthority
GrantedAuthority
s are high level permissions the user is granted. A few examples are roles or scopes.
GrantedAuthority
s can be obtained from the Authentication.getAuthorities()
method.
This method provides a Collection
of GrantedAuthority
objects.
A GrantedAuthority
is, not surprisingly, an authority that is granted to the principal.
Such authorities are usually "roles", such as ROLE_ADMINISTRATOR
or ROLE_HR_SUPERVISOR
.
These roles are later on configured for web authorization, method authorization and domain object authorization.
Other parts of Spring Security are capable of interpreting these authorities, and expect them to be present.
When using username/password based authentication GrantedAuthority
s are usually loaded by the UserDetailsService
.
Usually the GrantedAuthority
objects are application-wide permissions.
They are not specific to a given domain object.
Thus, you wouldn’t likely have a GrantedAuthority
to represent a permission to Employee
object number 54, because if there are thousands of such authorities you would quickly run out of memory (or, at the very least, cause the application to take a long time to authenticate a user).
Of course, Spring Security is expressly designed to handle this common requirement, but you’d instead use the project’s domain object security capabilities for this purpose.
AuthenticationManager
AuthenticationManager
is the API that defines how Spring Security’s Filters perform authentication.
The Authentication
that is returned is then set on the SecurityContextHolder by the controller (i.e. Spring Security’s Filters
s) that invoked the AuthenticationManager
.
If you are not integrating with Spring Security’s Filters
s you can set the SecurityContextHolder
directly and are not required to use an AuthenticationManager
.
While the implementation of AuthenticationManager
could be anything, the most common implementation is ProviderManager
.
ProviderManager
ProviderManager
is the most commonly used implementation of AuthenticationManager
.
ProviderManager
delegates to a List
of AuthenticationProvider
s.
Each AuthenticationProvider
has an opportunity to indicate that authentication should be successful, fail, or indicate it cannot make a decision and allow a downstream AuthenticationProvider
to decide.
If none of the configured AuthenticationProvider
s can authenticate, then authentication will fail with a ProviderNotFoundException
which is a special AuthenticationException
that indicates the ProviderManager
was not configured to support the type of Authentication
that was passed into it.
![providermanager](../../_images/servlet/authentication/architecture/providermanager.png)
In practice each AuthenticationProvider
knows how to perform a specific type of authentication.
For example, one AuthenticationProvider
might be able to validate a username/password, while another might be able to authenticate a SAML assertion.
This allows each AuthenticationProvider
to do a very specific type of authentication, while supporting multiple types of authentication and only exposing a single AuthenticationManager
bean.
ProviderManager
also allows configuring an optional parent AuthenticationManager
which is consulted in the event that no AuthenticationProvider
can perform authentication.
The parent can be any type of AuthenticationManager
, but it is often an instance of ProviderManager
.
![providermanager parent](../../_images/servlet/authentication/architecture/providermanager-parent.png)
In fact, multiple ProviderManager
instances might share the same parent AuthenticationManager
.
This is somewhat common in scenarios where there are multiple SecurityFilterChain
instances that have some authentication in common (the shared parent AuthenticationManager
), but also different authentication mechanisms (the different ProviderManager
instances).
![providermanagers parent](../../_images/servlet/authentication/architecture/providermanagers-parent.png)
By default ProviderManager
will attempt to clear any sensitive credentials information from the Authentication
object which is returned by a successful authentication request.
This prevents information like passwords being retained longer than necessary in the HttpSession
.
This may cause issues when you are using a cache of user objects, for example, to improve performance in a stateless application.
If the Authentication
contains a reference to an object in the cache (such as a UserDetails
instance) and this has its credentials removed, then it will no longer be possible to authenticate against the cached value.
You need to take this into account if you are using a cache.
An obvious solution is to make a copy of the object first, either in the cache implementation or in the AuthenticationProvider
which creates the returned Authentication
object.
Alternatively, you can disable the eraseCredentialsAfterAuthentication
property on ProviderManager
.
See the Javadoc for more information.
AuthenticationProvider
Multiple AuthenticationProvider
s can be injected into ProviderManager
.
Each AuthenticationProvider
performs a specific type of authentication.
For example, DaoAuthenticationProvider
supports username/password based authentication while JwtAuthenticationProvider
supports authenticating a JWT token.
Request Credentials with AuthenticationEntryPoint
AuthenticationEntryPoint
is used to send an HTTP response that requests credentials from a client.
Sometimes a client will proactively include credentials such as a username/password to request a resource. In these cases, Spring Security does not need to provide an HTTP response that requests credentials from the client since they are already included.
In other cases, a client will make an unauthenticated request to a resource that they are not authorized to access.
In this case, an implementation of AuthenticationEntryPoint
is used to request credentials from the client.
The AuthenticationEntryPoint
implementation might perform a redirect to a log in page, respond with an WWW-Authenticate header, etc.
AbstractAuthenticationProcessingFilter
AbstractAuthenticationProcessingFilter
is used as a base Filter
for authenticating a user’s credentials.
Before the credentials can be authenticated, Spring Security typically requests the credentials using AuthenticationEntryPoint
.
Next, the AbstractAuthenticationProcessingFilter
can authenticate any authentication requests that are submitted to it.
![abstractauthenticationprocessingfilter](../../_images/servlet/authentication/architecture/abstractauthenticationprocessingfilter.png)
When the user submits their credentials, the
AbstractAuthenticationProcessingFilter
creates an Authentication
from the HttpServletRequest
to be authenticated.
The type of Authentication
created depends on the subclass of AbstractAuthenticationProcessingFilter
.
For example, UsernamePasswordAuthenticationFilter
creates a UsernamePasswordAuthenticationToken
from a username and password that are submitted in the HttpServletRequest
.
Next, the
Authentication
is passed into the AuthenticationManager
to be authenticated.
If authentication fails, then Failure
-
The SecurityContextHolder is cleared out.
-
RememberMeServices.loginFail
is invoked. If remember me is not configured, this is a no-op. -
AuthenticationFailureHandler
is invoked.
If authentication is successful, then Success.
-
SessionAuthenticationStrategy
is notified of a new log in. -
The Authentication is set on the SecurityContextHolder. Later the
SecurityContextPersistenceFilter
saves theSecurityContext
to theHttpSession
. -
RememberMeServices.loginSuccess
is invoked. If remember me is not configured, this is a no-op. -
ApplicationEventPublisher
publishes anInteractiveAuthenticationSuccessEvent
. -
AuthenticationSuccessHandler
is invoked.