[[servlet-saml2login-logout]]
= Performing Single Logout

Among its xref:servlet/authentication/logout.adoc[other logout mechanisms], Spring Security ships with support for RP- and AP-initiated SAML 2.0 Single Logout.

Briefly, there are two use cases Spring Security supports:

* **RP-Initiated** - Your application has an endpoint that, when POSTed to, will logout the user and send a `saml2:LogoutRequest` to the asserting party.
Thereafter, the asserting party will send back a `saml2:LogoutResponse` and allow your application to respond
* **AP-Initiated** - Your application has an endpoint that will receive a `saml2:LogoutRequest` from the asserting party.
Your application will complete its logout at that point and then send a `saml2:LogoutResponse` to the asserting party.

[NOTE]
In the **AP-Initiated** scenario, any local redirection that your application would do post-logout is rendered moot.
Once your application sends a `saml2:LogoutResponse`, it no longer has control of the browser.

== Minimal Configuration for Single Logout

To use Spring Security's SAML 2.0 Single Logout feature, you will need the following things:

* First, the asserting party must support SAML 2.0 Single Logout
* Second, the asserting party should be configured to sign and POST `saml2:LogoutRequest` s and `saml2:LogoutResponse` s your application's `/logout/saml2/slo` endpoint
* Third, your application must have a PKCS#8 private key and X.509 certificate for signing `saml2:LogoutRequest` s and `saml2:LogoutResponse` s

You can achieve this in Spring Boot in the following way:

[source,yaml]
----
spring:
  security:
    saml2:
      relyingparty:
        registration:
          metadata:
            signing.credentials: <3>
              - private-key-location: classpath:credentials/rp-private.key
                certificate-location: classpath:credentials/rp-certificate.crt
            singlelogout.url: "{baseUrl}/logout/saml2/slo" <2>
            assertingparty:
              metadata-uri: https://ap.example.com/metadata <1>

----
<1> - The metadata URI of the IDP, which will indicate to your application its support of SLO
<2> - The SLO endpoint in your application
<3> - The signing credentials to sign ``<saml2:LogoutRequest>``s and ``<saml2:LogoutResponse>``s

[NOTE]
----
An asserting party supports Single Logout if their metadata includes the `<SingleLogoutService>` element in their metadata.
----

And that's it!

Spring Security's logout support offers a number of configuration points.
Consider the following use cases:

* Understand how the above <<_startup_expectations, minimal configuration works>>
* Get a picture of <<architecture, the overall architecture>>
* Allow users to <<separating-local-saml2-logout, logout out of the app only>>
* Customize <<_configuring_logout_endpoints, logout endpoints>>
* Storing `<saml2:LogoutRequests>` somewhere <<_customizing_storage, other than the session>>

=== Startup Expectations

When these properties are used, in addition to login, SAML 2.0 Service Provider will automatically configure itself facilitate logout by way of ``<saml2:LogoutRequest>``s and ``<saml2:LogoutResponse>``s using either RP- or AP-initiated logout.

It achieves this through a deterministic startup process:

1. Query the Identity Server Metadata endpoint for the `<SingleLogoutService>` element
2. Scan the metadata and cache any public signature verification keys
3. Prepare the appropriate endpoints

A consequence of this process is that the identity server must be up and receiving requests in order for Service Provider to successfully start up.

[NOTE]
If the identity server is down when Service Provider queries it (given appropriate timeouts), then startup will fail.

=== Runtime Expectations

Given the above configuration any logged-in user can send a `POST /logout` to your application to perform RP-initiated SLO.
Your application will then do the following:

1. Logout the user and invalidate the session
2. Produce a `<saml2:LogoutRequest>` and POST it to the associated asserting party's SLO endpoint
3. Then, if the asserting party responds with a `<saml2:LogoutResponse>`, the application with verify it and redirect to the configured success endpoint

Also, your application can participate in an AP-initiated logout when the asserting party sends a `<saml2:LogoutRequest>` to `/logout/saml2/slo`.
When this happens, your application will do the following:

1. Verify the `<saml2:LogoutRequest>`
2. Logout the user and invalidate the session
3. Produce a `<saml2:LogoutResponse>` and POST it back to the asserting party's SLO endpoint

== Minimal Configuration Sans Boot

Instead of Boot properties, you can also achieve the same outcome by publishing the beans directly like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Configuration
public class SecurityConfig {
    @Value("${private.key}") RSAPrivateKey key;
    @Value("${public.certificate}") X509Certificate certificate;

    @Bean
    RelyingPartyRegistrationRepository registrations() {
        Saml2X509Credential credential = Saml2X509Credential.signing(key, certificate);
        RelyingPartyRegistration registration = RelyingPartyRegistrations
                .fromMetadataLocation("https://ap.example.org/metadata") <1>
                .registrationId("metadata")
                .singleLogoutServiceLocation("{baseUrl}/logout/saml2/slo") <2>
                .signingX509Credentials((signing) -> signing.add(credential)) <3>
                .build();
        return new InMemoryRelyingPartyRegistrationRepository(registration);
    }

    @Bean
    SecurityFilterChain web(HttpSecurity http) throws Exception {
        http
            .authorizeHttpRequests((authorize) -> authorize
                .anyRequest().authenticated()
            )
            .saml2Login(withDefaults())
            .saml2Logout(withDefaults()); <4>

        return http.build();
    }
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Configuration
class SecurityConfig(@Value("${private.key}") val key: RSAPrivateKey,
        @Value("${public.certificate}") val certificate: X509Certificate) {

    @Bean
    fun registrations(): RelyingPartyRegistrationRepository {
        val credential = Saml2X509Credential.signing(key, certificate)
        val registration = RelyingPartyRegistrations
                .fromMetadataLocation("https://ap.example.org/metadata") <1>
                .registrationId("metadata")
                .singleLogoutServiceLocation("{baseUrl}/logout/saml2/slo") <2>
                .signingX509Credentials({ signing: List<Saml2X509Credential> -> signing.add(credential) }) <3>
                .build()
        return InMemoryRelyingPartyRegistrationRepository(registration)
    }

    @Bean
    fun web(http: HttpSecurity): SecurityFilterChain {
        http {
            authorizeHttpRequests {
                anyRequest = authenticated
            }
            saml2Login {

            }
            saml2Logout { <4>

            }
        }

        return http.build()
    }
}
----
======
<1> - The metadata URI of the IDP, which will indicate to your application its support of SLO
<2> - The SLO endpoint in your application
<3> - The signing credentials to sign ``<saml2:LogoutRequest>``s and ``<saml2:LogoutResponse>``s, which you can also add to xref:servlet/saml2/login/overview.adoc#servlet-saml2login-rpr-duplicated[multiple relying parties]
<4> - Second, indicate that your application wants to use SAML SLO to logout the end user

[NOTE]
Adding `saml2Logout` adds the capability for logout to your service provider as a whole.
Because it is an optional capability, you need to enable it for each individual `RelyingPartyRegistration`.
You do this by setting the `RelyingPartyRegistration.Builder#singleLogoutServiceLocation` property as seen above.

[[architecture]]
== How Saml 2.0 Logout Works

Next, let's see the architectural components that Spring Security uses to support https://docs.oasis-open.org/security/saml/v2.0/saml-profiles-2.0-os.pdf#page=37[SAML 2.0 Logout] in servlet-based applications, like the one we just saw.

For RP-initiated logout:

image:{icondir}/number_1.png[] Spring Security executes its xref:servlet/authentication/logout.adoc#logout-architecture[logout flow], calling its ``LogoutHandler``s to invalidate the session and perform other cleanup.
It then invokes the javadoc:org.springframework.security.saml2.provider.service.web.authentication.logout.Saml2RelyingPartyInitiatedLogoutSuccessHandler[].

image:{icondir}/number_2.png[] The logout success handler uses an instance of
javadoc:org.springframework.security.saml2.provider.service.web.authentication.logout.Saml2LogoutRequestResolver[] to create, sign, and serialize a `<saml2:LogoutRequest>`.
It uses the keys and configuration from the xref:servlet/saml2/login/overview.adoc#servlet-saml2login-relyingpartyregistration[`RelyingPartyRegistration`] that is associated with the current `Saml2AuthenticatedPrincipal`.
Then, it redirect-POSTs the `<saml2:LogoutRequest>` to the asserting party SLO endpoint

The browser hands control over to the asserting party.
If the asserting party redirects back (which it may not), then the application proceeds to step image:{icondir}/number_3.png[].

image:{icondir}/number_3.png[] The javadoc:org.springframework.security.saml2.provider.service.web.authentication.logout.Saml2LogoutResponseFilter[] deserializes, verifies, and processes the `<saml2:LogoutResponse>` with its javadoc:org.springframework.security.saml2.provider.service.authentication.logout.Saml2LogoutResponseValidator[].

image:{icondir}/number_4.png[] If valid, then it completes the local logout flow by redirecting to `/login?logout`, or whatever has been configured.
If invalid, then it responds with a 400.

For AP-initiated logout:

image:{icondir}/number_1.png[] The javadoc:org.springframework.security.saml2.provider.service.web.authentication.logout.Saml2LogoutRequestFilter[] deserializes, verifies, and processes the `<saml2:LogoutRequest>` with its javadoc:org.springframework.security.saml2.provider.service.authentication.logout.Saml2LogoutRequestValidator[].

image:{icondir}/number_2.png[] If valid, then the filter calls the configured ``LogoutHandler``s, invalidating the session and performing other cleanup.

image:{icondir}/number_3.png[] It uses a javadoc:org.springframework.security.saml2.provider.service.web.authentication.logout.Saml2LogoutResponseResolver[] to create, sign and serialize a `<saml2:LogoutResponse>`.
It uses the keys and configuration from the xref:servlet/saml2/login/overview.adoc#servlet-saml2login-relyingpartyregistration[`RelyingPartyRegistration`] derived from the endpoint or from the contents of the `<saml2:LogoutRequest>`.
Then, it redirect-POSTs the `<saml2:LogoutResponse>` to the asserting party SLO endpoint.

The browser hands control over to the asserting party.

image:{icondir}/number_4.png[] If invalid, then it https://github.com/spring-projects/spring-security/pull/14676[responds with a 400].

== Configuring Logout Endpoints

There are three behaviors that can be triggered by different endpoints:

* RP-initiated logout, which allows an authenticated user to `POST` and trigger the logout process by sending the asserting party a `<saml2:LogoutRequest>`
* AP-initiated logout, which allows an asserting party to send a `<saml2:LogoutRequest>` to the application
* AP logout response, which allows an asserting party to send a `<saml2:LogoutResponse>` in response to the RP-initiated `<saml2:LogoutRequest>`

The first is triggered by performing normal `POST /logout` when the principal is of type `Saml2AuthenticatedPrincipal`.

The second is triggered by POSTing to the `/logout/saml2/slo` endpoint with a `SAMLRequest` signed by the asserting party.

The third is triggered by POSTing to the `/logout/saml2/slo` endpoint with a `SAMLResponse` signed by the asserting party.

Because the user is already logged in or the original Logout Request is known, the `registrationId` is already known.
For this reason, `+{registrationId}+` is not part of these URLs by default.

This URL is customizable in the DSL.

For example, if you are migrating your existing relying party over to Spring Security, your asserting party may already be pointing to `GET /SLOService.saml2`.
To reduce changes in configuration for the asserting party, you can configure the filter in the DSL like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutRequest((request) -> request.logoutUrl("/SLOService.saml2"))
        .logoutResponse((response) -> response.logoutUrl("/SLOService.saml2"))
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutRequest {
            logoutUrl = "/SLOService.saml2"
        }
        logoutResponse {
            logoutUrl = "/SLOService.saml2"
        }
    }
}
----
======

You should also configure these endpoints in your `RelyingPartyRegistration`.

Also, you can customize the endpoint for triggering logout locally like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2.logoutUrl("/saml2/logout"));
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutUrl = "/saml2/logout"
    }
}
----
======

[[separating-local-saml2-logout]]
=== Separating Local Logout from SAML 2.0 Logout

In some cases, you may want to expose one logout endpoint for local logout and another for RP-initiated SLO.
Like is the case with other logout mechanisms, you can register more than one, so long as they each have a different endpoint.

So, for example, you can wire the DSL like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .logout((logout) -> logout.logoutUrl("/logout"))
    .saml2Logout((saml2) -> saml2.logoutUrl("/saml2/logout"));
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    logout {
        logoutUrl = "/logout"
    }
    saml2Logout {
        logoutUrl = "/saml2/logout"
    }
}
----
======

and now if a client sends a `POST /logout`, the session will be cleared, but there won't be a `<saml2:LogoutRequest>` sent to the asserting party.
But, if the client sends a `POST /saml2/logout`, then the application will initiate SAML 2.0 SLO as normal.

== Customizing `<saml2:LogoutRequest>` Resolution

It's common to need to set other values in the `<saml2:LogoutRequest>` than the defaults that Spring Security provides.

By default, Spring Security will issue a `<saml2:LogoutRequest>` and supply:

* The `Destination` attribute - from `RelyingPartyRegistration#getAssertingPartyMetadata#getSingleLogoutServiceLocation`
* The `ID` attribute - a GUID
* The `<Issuer>` element - from `RelyingPartyRegistration#getEntityId`
* The `<NameID>` element - from `Authentication#getName`

To add other values, you can use delegation, like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
Saml2LogoutRequestResolver logoutRequestResolver(RelyingPartyRegistrationRepository registrations) {
	OpenSaml4LogoutRequestResolver logoutRequestResolver =
			new OpenSaml4LogoutRequestResolver(registrations);
	logoutRequestResolver.setParametersConsumer((parameters) -> {
		String name = ((Saml2AuthenticatedPrincipal) parameters.getAuthentication().getPrincipal()).getFirstAttribute("CustomAttribute");
		String format = "urn:oasis:names:tc:SAML:2.0:nameid-format:transient";
		LogoutRequest logoutRequest = parameters.getLogoutRequest();
		NameID nameId = logoutRequest.getNameID();
		nameId.setValue(name);
		nameId.setFormat(format);
	});
	return logoutRequestResolver;
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
open fun logoutRequestResolver(registrations:RelyingPartyRegistrationRepository?): Saml2LogoutRequestResolver {
    val logoutRequestResolver = OpenSaml4LogoutRequestResolver(registrations)
    logoutRequestResolver.setParametersConsumer { parameters: LogoutRequestParameters ->
        val name: String = (parameters.getAuthentication().getPrincipal() as Saml2AuthenticatedPrincipal).getFirstAttribute("CustomAttribute")
        val format = "urn:oasis:names:tc:SAML:2.0:nameid-format:transient"
        val logoutRequest: LogoutRequest = parameters.getLogoutRequest()
        val nameId: NameID = logoutRequest.getNameID()
        nameId.setValue(name)
        nameId.setFormat(format)
    }
    return logoutRequestResolver
}
----
======

Then, you can supply your custom `Saml2LogoutRequestResolver` in the DSL as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutRequest((request) -> request
            .logoutRequestResolver(this.logoutRequestResolver)
        )
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutRequest {
            logoutRequestResolver = this.logoutRequestResolver
        }
    }
}
----
======

== Customizing `<saml2:LogoutResponse>` Resolution

It's common to need to set other values in the `<saml2:LogoutResponse>` than the defaults that Spring Security provides.

By default, Spring Security will issue a `<saml2:LogoutResponse>` and supply:

* The `Destination` attribute - from `RelyingPartyRegistration#getAssertingPartyMetadata#getSingleLogoutServiceResponseLocation`
* The `ID` attribute - a GUID
* The `<Issuer>` element - from `RelyingPartyRegistration#getEntityId`
* The `<Status>` element - `SUCCESS`

To add other values, you can use delegation, like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Bean
public Saml2LogoutResponseResolver logoutResponseResolver(RelyingPartyRegistrationRepository registrations) {
	OpenSaml4LogoutResponseResolver logoutRequestResolver =
			new OpenSaml4LogoutResponseResolver(registrations);
	logoutRequestResolver.setParametersConsumer((parameters) -> {
		if (checkOtherPrevailingConditions(parameters.getRequest())) {
			parameters.getLogoutRequest().getStatus().getStatusCode().setCode(StatusCode.PARTIAL_LOGOUT);
		}
	});
	return logoutRequestResolver;
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Bean
open fun logoutResponseResolver(registrations: RelyingPartyRegistrationRepository?): Saml2LogoutResponseResolver {
    val logoutRequestResolver = OpenSaml4LogoutResponseResolver(registrations)
    logoutRequestResolver.setParametersConsumer { LogoutResponseParameters parameters ->
        if (checkOtherPrevailingConditions(parameters.getRequest())) {
            parameters.getLogoutRequest().getStatus().getStatusCode().setCode(StatusCode.PARTIAL_LOGOUT)
        }
    }
    return logoutRequestResolver
}
----
======

Then, you can supply your custom `Saml2LogoutResponseResolver` in the DSL as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutRequest((request) -> request
            .logoutRequestResolver(this.logoutRequestResolver)
        )
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutRequest {
            logoutRequestResolver = this.logoutRequestResolver
        }
    }
}
----
======

== Customizing `<saml2:LogoutRequest>` Authentication

To customize validation, you can implement your own `Saml2LogoutRequestValidator`.
At this point, the validation is minimal, so you may be able to first delegate to the default `Saml2LogoutRequestValidator` like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Component
public class MyOpenSamlLogoutRequestValidator implements Saml2LogoutRequestValidator {
	private final Saml2LogoutRequestValidator delegate = new OpenSamlLogoutRequestValidator();

	@Override
    public Saml2LogoutRequestValidator logout(Saml2LogoutRequestValidatorParameters parameters) {
		 // verify signature, issuer, destination, and principal name
		Saml2LogoutValidatorResult result = delegate.authenticate(authentication);

		LogoutRequest logoutRequest = // ... parse using OpenSAML
        // perform custom validation
    }
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Component
open class MyOpenSamlLogoutRequestValidator: Saml2LogoutRequestValidator {
	private val delegate = OpenSamlLogoutRequestValidator()

	@Override
    fun logout(parameters: Saml2LogoutRequestValidatorParameters): Saml2LogoutRequestValidator {
		 // verify signature, issuer, destination, and principal name
		val result = delegate.authenticate(authentication)

		val logoutRequest: LogoutRequest = // ... parse using OpenSAML
        // perform custom validation
    }
}
----
======

Then, you can supply your custom `Saml2LogoutRequestValidator` in the DSL as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutRequest((request) -> request
            .logoutRequestValidator(myOpenSamlLogoutRequestValidator)
        )
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutRequest {
            logoutRequestValidator = myOpenSamlLogoutRequestValidator
        }
    }
}
----
======

== Customizing `<saml2:LogoutResponse>` Authentication

To customize validation, you can implement your own `Saml2LogoutResponseValidator`.
At this point, the validation is minimal, so you may be able to first delegate to the default `Saml2LogoutResponseValidator` like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
@Component
public class MyOpenSamlLogoutResponseValidator implements Saml2LogoutResponseValidator {
	private final Saml2LogoutResponseValidator delegate = new OpenSamlLogoutResponseValidator();

	@Override
    public Saml2LogoutValidatorResult logout(Saml2LogoutResponseValidatorParameters parameters) {
		// verify signature, issuer, destination, and status
		Saml2LogoutValidatorResult result = delegate.authenticate(parameters);

		LogoutResponse logoutResponse = // ... parse using OpenSAML
        // perform custom validation
    }
}
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
@Component
open class MyOpenSamlLogoutResponseValidator: Saml2LogoutResponseValidator {
	private val delegate = OpenSaml4LogoutResponseValidator()

	@Override
    fun logout(parameters: Saml2LogoutResponseValidatorParameters): Saml2LogoutResponseValidator {
		// verify signature, issuer, destination, and status
		val result = delegate.authenticate(authentication)

		val logoutResponse: LogoutResponse = // ... parse using OpenSAML
        // perform custom validation
    }
}
----
======

Then, you can supply your custom `Saml2LogoutResponseValidator` in the DSL as follows:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutResponse((response) -> response
            .logoutResponseAuthenticator(myOpenSamlLogoutResponseAuthenticator)
        )
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutResponse {
            logoutResponseValidator = myOpenSamlLogoutResponseValidator
        }
    }
}
----
======

== Customizing `<saml2:LogoutRequest>` storage

When your application sends a `<saml2:LogoutRequest>`, the value is stored in the session so that the `RelayState` parameter and the `InResponseTo` attribute in the `<saml2:LogoutResponse>` can be verified.

If you want to store logout requests in some place other than the session, you can supply your custom implementation in the DSL, like so:

[tabs]
======
Java::
+
[source,java,role="primary"]
----
http
    .saml2Logout((saml2) -> saml2
        .logoutRequest((request) -> request
            .logoutRequestRepository(myCustomLogoutRequestRepository)
        )
    );
----

Kotlin::
+
[source,kotlin,role="secondary"]
----
http {
    saml2Logout {
        logoutRequest {
            logoutRequestRepository = myCustomLogoutRequestRepository
        }
    }
}
----
======

[[jc-logout-references]]
== Further Logout-Related References

- xref:servlet/test/mockmvc/logout.adoc#test-logout[Testing Logout]
- xref:servlet/integrations/servlet-api.adoc#servletapi-logout[HttpServletRequest.logout()]
- xref:servlet/exploits/csrf.adoc#csrf-considerations-logout[Logging Out] in section CSRF Caveats
