SpringBoot RelyingPartyRegistrationRepository is null when configuring SAML2 via application.yaml in Spring Boot 4.0.0 and later

Description

When trying to configure SAML2 using the auto-configuration via application.yaml in Spring Boot 4.0.0 or later, I encounter the following exception: Factory method 'securityFilterChain' threw exception with message: relyingPartyRegistrationRepository cannot be null. It seems that the configuration from application.yaml is not being loaded properly.

Steps to Reproduce

1. Add Maven Repository and Dependency

pom.xml:

<repositories>
    <repository>
        <id>shibboleth-releases</id>
        <name>Shibboleth Releases Repository</name>
        <url>https://build.shibboleth.net/maven/releases/</url>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
    </repository>
</repositories>

<dependencies>
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-saml2-service-provider</artifactId>
    </dependency>
</dependencies>
````

---

### 2. Configure SAML2 in `application.yaml`
Example :

```yaml
spring:
  security:
    saml2:
      relyingparty:
        registration:
          idp:
            entity-id: "http://localhost:8081/saml2/metadata"
            acs:
              location: "http://localhost:8081/login/saml2/sso"
            signing:
              credentials:
                - private-key-location: classpath:credentials/rp-private-pkcs8.key
                  certificate-location: classpath:credentials/rp-certificate.crt
            singlelogout:
              binding: REDIRECT
              url: "http://localhost:8081/logout/saml2/slo"
            assertingparty:
              metadata-uri: "http://localhost:8080/realms/idp_realm/protocol/saml/descriptor"
              verification:
                credentials:
                  - certificate-location: "classpath:credentials/ipd-signing.crt"

---

3. Security Configuration

Example:

@Bean
public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
    http
            .authorizeHttpRequests(auth -> auth
                    .anyRequest().authenticated()
            )
            .saml2Login(Customizer.withDefaults());

    return http.build();
}

---

4. Run the Application

Error occurs:

Factory method 'securityFilterChain' threw exception with message:
relyingPartyRegistrationRepository cannot be null

---

5. Manual Configuration Works (For Comparison)

If you define the repository manually, the application works correctly:

 @Bean
 public RelyingPartyRegistrationRepository relyingPartyRegistrationRepository() {
     RelyingPartyRegistration registration = RelyingPartyRegistration
             .withRegistrationId("idp")
             .entityId("http://localhost:8081/saml2/metadata")
             .assertionConsumerServiceLocation("http://localhost:8081/login/saml2/sso")
             .singleLogoutServiceBinding(REDIRECT)
             .singleLogoutServiceLocation("http://localhost:8081/logout/saml2/slo")
             .signingX509Credentials(c -> c.add(spSigningCredential()))
             .assertingPartyMetadata(party -> party
                     .entityId("http://localhost:8080/realms/idp_realm")
                     .singleSignOnServiceLocation("http://localhost:8080/realms/idp_realm/protocol/saml")
                     .verificationX509Credentials(c -> c.add(idpVerifyingCredential()))
                     .wantAuthnRequestsSigned(true))
             .build();

     return new InMemoryRelyingPartyRegistrationRepository(registration);
 }

With this explicit bean, SAML2 login works fully, confirming that the issue is specifically with auto-configuration not loading YAML properties.

Expected Behavior

The RelyingPartyRegistrationRepository should be automatically created from the YAML configuration, and the application should start without throwing an exception.

Actual Behavior

The application fails to start with the exception: Factory method 'securityFilterChain' threw exception with message: relyingPartyRegistrationRepository cannot be null

Comment From: wilkinsona

Judging by the small pom.xml snippet that you have shared, I suspect you're missing a dependency on spring-boot-security-saml2. It can be added in place of your dependency on spring-security-saml2-service-provider.

Comment From: M313K

Thanks a lot! After going through the dependencies, spring-boot-starter-security-saml2 was missing.

Appreciate your help!