[[servlet-saml2login-authenticate-responses]]
= Authenticating ``<saml2:Response>``s

To verify SAML 2.0 Responses, Spring Security uses xref:servlet/saml2/login/overview.adoc#servlet-saml2login-architecture[`OpenSaml4AuthenticationProvider`] by default.

You can configure this in a number of ways including:

1. Setting a clock skew to timestamp validation
2. Mapping the response to a list of `GrantedAuthority` instances
3. Customizing the strategy for validating assertions
4. Customizing the strategy for decrypting response and assertion elements

To configure these, you'll use the `saml2Login#authenticationManager` method in the DSL.

[[servlet-saml2login-opensamlauthenticationprovider-clockskew]]
== Setting a Clock Skew

It's not uncommon for the asserting and relying parties to have system clocks that aren't perfectly synchronized.
For that reason, you can configure `OpenSaml4AuthenticationProvider` 's default assertion validator with some tolerance:

====
.Java
[source,java,role="primary"]
----
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        OpenSaml4AuthenticationProvider authenticationProvider = new OpenSaml4AuthenticationProvider();
        authenticationProvider.setAssertionValidator(OpenSaml4AuthenticationProvider
                .createDefaultAssertionValidator(assertionToken -> {
                    Map<String, Object> params = new HashMap<>();
                    params.put(CLOCK_SKEW, Duration.ofMinutes(10).toMillis());
                    // ... other validation parameters
                    return new ValidationContext(params);
                })
        );

        http
            .authorizeHttpRequests(authz -> authz
                .anyRequest().authenticated()
            )
            .saml2Login(saml2 -> saml2
                .authenticationManager(new ProviderManager(authenticationProvider))
            );
    }
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@EnableWebSecurity
open class SecurityConfig : WebSecurityConfigurerAdapter() {
    override fun configure(http: HttpSecurity) {
        val authenticationProvider = OpenSaml4AuthenticationProvider()
        authenticationProvider.setAssertionValidator(
            OpenSaml4AuthenticationProvider
                .createDefaultAssertionValidator(Converter<OpenSaml4AuthenticationProvider.AssertionToken, ValidationContext> {
                    val params: MutableMap<String, Any> = HashMap()
                    params[CLOCK_SKEW] =
                        Duration.ofMinutes(10).toMillis()
                    ValidationContext(params)
                })
        )
        http {
            authorizeRequests {
                authorize(anyRequest, authenticated)
            }
            saml2Login {
                authenticationManager = ProviderManager(authenticationProvider)
            }
        }
    }
}
----
====

[[servlet-saml2login-opensamlauthenticationprovider-userdetailsservice]]
== Coordinating with a `UserDetailsService`

Or, perhaps you would like to include user details from a legacy `UserDetailsService`.
In that case, the response authentication converter can come in handy, as can be seen below:

====
.Java
[source,java,role="primary"]
----
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Autowired
    UserDetailsService userDetailsService;

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        OpenSaml4AuthenticationProvider authenticationProvider = new OpenSaml4AuthenticationProvider();
        authenticationProvider.setResponseAuthenticationConverter(responseToken -> {
            Saml2Authentication authentication = OpenSaml4AuthenticationProvider
                    .createDefaultResponseAuthenticationConverter() <1>
                    .convert(responseToken);
            Assertion assertion = responseToken.getResponse().getAssertions().get(0);
            String username = assertion.getSubject().getNameID().getValue();
            UserDetails userDetails = this.userDetailsService.loadUserByUsername(username); <2>
            return MySaml2Authentication(userDetails, authentication); <3>
        });

        http
            .authorizeHttpRequests(authz -> authz
                .anyRequest().authenticated()
            )
            .saml2Login(saml2 -> saml2
                .authenticationManager(new ProviderManager(authenticationProvider))
            );
    }
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@EnableWebSecurity
open class SecurityConfig : WebSecurityConfigurerAdapter() {
    @Autowired
    var userDetailsService: UserDetailsService? = null

    override fun configure(http: HttpSecurity) {
        val authenticationProvider = OpenSaml4AuthenticationProvider()
        authenticationProvider.setResponseAuthenticationConverter { responseToken: OpenSaml4AuthenticationProvider.ResponseToken ->
            val authentication = OpenSaml4AuthenticationProvider
                .createDefaultResponseAuthenticationConverter() <1>
                .convert(responseToken)
            val assertion: Assertion = responseToken.response.assertions[0]
            val username: String = assertion.subject.nameID.value
            val userDetails = userDetailsService!!.loadUserByUsername(username) <2>
            MySaml2Authentication(userDetails, authentication) <3>
        }
        http {
            authorizeRequests {
                authorize(anyRequest, authenticated)
            }
            saml2Login {
                authenticationManager = ProviderManager(authenticationProvider)
            }
        }
    }
}
----
====
<1> First, call the default converter, which extracts attributes and authorities from the response
<2> Second, call the xref:servlet/authentication/passwords/user-details-service.adoc#servlet-authentication-userdetailsservice[`UserDetailsService`] using the relevant information
<3> Third, return a custom authentication that includes the user details

[NOTE]
It's not required to call `OpenSaml4AuthenticationProvider` 's default authentication converter.
It returns a `Saml2AuthenticatedPrincipal` containing the attributes it extracted from ``AttributeStatement``s as well as the single `ROLE_USER` authority.

[[servlet-saml2login-opensamlauthenticationprovider-additionalvalidation]]
== Performing Additional Response Validation

`OpenSaml4AuthenticationProvider` validates the `Issuer` and `Destination` values right after decrypting the `Response`.
You can customize the validation by extending the default validator concatenating with your own response validator, or you can replace it entirely with yours.

For example, you can throw a custom exception with any additional information available in the `Response` object, like so:
[source,java]
----
OpenSaml4AuthenticationProvider provider = new OpenSaml4AuthenticationProvider();
provider.setResponseValidator((responseToken) -> {
	Saml2ResponseValidatorResult result = OpenSamlAuthenticationProvider
		.createDefaultResponseValidator()
		.convert(responseToken)
		.concat(myCustomValidator.convert(responseToken));
	if (!result.getErrors().isEmpty()) {
		String inResponseTo = responseToken.getInResponseTo();
		throw new CustomSaml2AuthenticationException(result, inResponseTo);
	}
	return result;
});
----

== Performing Additional Assertion Validation
`OpenSaml4AuthenticationProvider` performs minimal validation on SAML 2.0 Assertions.
After verifying the signature, it will:

1. Validate `<AudienceRestriction>` and `<DelegationRestriction>` conditions
2. Validate ``<SubjectConfirmation>``s, expect for any IP address information

To perform additional validation, you can configure your own assertion validator that delegates to `OpenSaml4AuthenticationProvider` 's default and then performs its own.

[[servlet-saml2login-opensamlauthenticationprovider-onetimeuse]]
For example, you can use OpenSAML's `OneTimeUseConditionValidator` to also validate a `<OneTimeUse>` condition, like so:

====
.Java
[source,java,role="primary"]
----
OpenSaml4AuthenticationProvider provider = new OpenSaml4AuthenticationProvider();
OneTimeUseConditionValidator validator = ...;
provider.setAssertionValidator(assertionToken -> {
    Saml2ResponseValidatorResult result = OpenSaml4AuthenticationProvider
            .createDefaultAssertionValidator()
            .convert(assertionToken);
    Assertion assertion = assertionToken.getAssertion();
    OneTimeUse oneTimeUse = assertion.getConditions().getOneTimeUse();
    ValidationContext context = new ValidationContext();
    try {
        if (validator.validate(oneTimeUse, assertion, context) = ValidationResult.VALID) {
            return result;
        }
    } catch (Exception e) {
        return result.concat(new Saml2Error(INVALID_ASSERTION, e.getMessage()));
    }
    return result.concat(new Saml2Error(INVALID_ASSERTION, context.getValidationFailureMessage()));
});
----

.Kotlin
[source,kotlin,role="secondary"]
----
var provider = OpenSaml4AuthenticationProvider()
var validator: OneTimeUseConditionValidator = ...
provider.setAssertionValidator { assertionToken ->
    val result = OpenSaml4AuthenticationProvider
        .createDefaultAssertionValidator()
        .convert(assertionToken)
    val assertion: Assertion = assertionToken.assertion
    val oneTimeUse: OneTimeUse = assertion.conditions.oneTimeUse
    val context = ValidationContext()
    try {
        if (validator.validate(oneTimeUse, assertion, context) = ValidationResult.VALID) {
            return@setAssertionValidator result
        }
    } catch (e: Exception) {
        return@setAssertionValidator result.concat(Saml2Error(INVALID_ASSERTION, e.message))
    }
    result.concat(Saml2Error(INVALID_ASSERTION, context.validationFailureMessage))
}
----
====

[NOTE]
While recommended, it's not necessary to call `OpenSaml4AuthenticationProvider` 's default assertion validator.
A circumstance where you would skip it would be if you don't need it to check the `<AudienceRestriction>` or the `<SubjectConfirmation>` since you are doing those yourself.

[[servlet-saml2login-opensamlauthenticationprovider-decryption]]
== Customizing Decryption

Spring Security decrypts `<saml2:EncryptedAssertion>`, `<saml2:EncryptedAttribute>`, and `<saml2:EncryptedID>` elements automatically by using the decryption xref:servlet/saml2/login/overview.adoc#servlet-saml2login-rpr-credentials[`Saml2X509Credential` instances] registered in the xref:servlet/saml2/login/overview.adoc#servlet-saml2login-relyingpartyregistration[`RelyingPartyRegistration`].

`OpenSaml4AuthenticationProvider` exposes xref:servlet/saml2/login/overview.adoc#servlet-saml2login-architecture[two decryption strategies].
The response decrypter is for decrypting encrypted elements of the `<saml2:Response>`, like `<saml2:EncryptedAssertion>`.
The assertion decrypter is for decrypting encrypted elements of the `<saml2:Assertion>`, like `<saml2:EncryptedAttribute>` and `<saml2:EncryptedID>`.

You can replace `OpenSaml4AuthenticationProvider`'s default decryption strategy with your own.
For example, if you have a separate service that decrypts the assertions in a `<saml2:Response>`, you can use it instead like so:

====
.Java
[source,java,role="primary"]
----
MyDecryptionService decryptionService = ...;
OpenSaml4AuthenticationProvider provider = new OpenSaml4AuthenticationProvider();
provider.setResponseElementsDecrypter((responseToken) -> decryptionService.decrypt(responseToken.getResponse()));
----

.Kotlin
[source,kotlin,role="secondary"]
----
val decryptionService: MyDecryptionService = ...
val provider = OpenSaml4AuthenticationProvider()
provider.setResponseElementsDecrypter { responseToken -> decryptionService.decrypt(responseToken.response) }
----
====

If you are also decrypting individual elements in a `<saml2:Assertion>`, you can customize the assertion decrypter, too:

====
.Java
[source,java,role="primary"]
----
provider.setAssertionElementsDecrypter((assertionToken) -> decryptionService.decrypt(assertionToken.getAssertion()));
----

.Kotlin
[source,kotlin,role="secondary"]
----
provider.setAssertionElementsDecrypter { assertionToken -> decryptionService.decrypt(assertionToken.assertion) }
----
====

NOTE: There are two separate decrypters since assertions can be signed separately from responses.
Trying to decrypt a signed assertion's elements before signature verification may invalidate the signature.
If your asserting party signs the response only, then it's safe to decrypt all elements using only the response decrypter.

[[servlet-saml2login-authenticationmanager-custom]]
== Using a Custom Authentication Manager

[[servlet-saml2login-opensamlauthenticationprovider-authenticationmanager]]
Of course, the `authenticationManager` DSL method can be also used to perform a completely custom SAML 2.0 authentication.
This authentication manager should expect a `Saml2AuthenticationToken` object containing the SAML 2.0 Response XML data.

====
.Java
[source,java,role="primary"]
----
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        AuthenticationManager authenticationManager = new MySaml2AuthenticationManager(...);
        http
            .authorizeHttpRequests(authorize -> authorize
                .anyRequest().authenticated()
            )
            .saml2Login(saml2 -> saml2
                .authenticationManager(authenticationManager)
            )
        ;
    }
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@EnableWebSecurity
open class SecurityConfig : WebSecurityConfigurerAdapter() {
    override fun configure(http: HttpSecurity) {
        val customAuthenticationManager: AuthenticationManager = MySaml2AuthenticationManager(...)
        http {
            authorizeRequests {
                authorize(anyRequest, authenticated)
            }
            saml2Login {
                authenticationManager = customAuthenticationManager
            }
        }
    }
}
----
====

[[servlet-saml2login-authenticatedprincipal]]
== Using `Saml2AuthenticatedPrincipal`

With the relying party correctly configured for a given asserting party, it's ready to accept assertions.
Once the relying party validates an assertion, the result is a `Saml2Authentication` with a `Saml2AuthenticatedPrincipal`.

This means that you can access the principal in your controller like so:

====
.Java
[source,java,role="primary"]
----
@Controller
public class MainController {
	@GetMapping("/")
	public String index(@AuthenticationPrincipal Saml2AuthenticatedPrincipal principal, Model model) {
		String email = principal.getFirstAttribute("email");
		model.setAttribute("email", email);
		return "index";
	}
}
----

.Kotlin
[source,kotlin,role="secondary"]
----
@Controller
class MainController {
    @GetMapping("/")
    fun index(@AuthenticationPrincipal principal: Saml2AuthenticatedPrincipal, model: Model): String {
        val email = principal.getFirstAttribute<String>("email")
        model.setAttribute("email", email)
        return "index"
    }
}
----
====

[TIP]
Because the SAML 2.0 specification allows for each attribute to have multiple values, you can either call `getAttribute` to get the list of attributes or `getFirstAttribute` to get the first in the list.
`getFirstAttribute` is quite handy when you know that there is only one value.
