Mocking OAuth2 client with WebTestClient for servlet applications results in null httpHandlerBuilder

Question

My Spring Boot application acts as an OAuth2 client by using the spring-boot-starter-oauth2-client dependency.

Now I'd like to write an integration test (@SpringBootTest) to verify the behavior of a REST endpoint secured by OAuth2. The Testing OAuth 2.0 Clients documentation describes that it is possible to use mutateWith(mockOAuth2Client()) to mock a login via OAuth2.

public class UserIT {

  @Autowired
  private WebTestClient webTestClient;

  @Test
  void test() {
    webTestClient
      .mutateWith(mockOAuth2Client("keycloak"))
      .get()
      .uri("/api/user/1345")
      .exchange()
      .expectStatus().isOk();
  }
}

However, the test fails with the following message:

java.lang.NullPointerException: Cannot invoke "org.springframework.web.server.adapter.WebHttpHandlerBuilder.filters(java.util.function.Consumer)" because "httpHandlerBuilder" is null
    at org.springframework.security.test.web.reactive.server.SecurityMockServerConfigurers$OAuth2ClientMutator.afterConfigurerAdded(SecurityMockServerConfigurers.java:1113)
    at org.springframework.test.web.reactive.server.DefaultWebTestClientBuilder.apply(DefaultWebTestClientBuilder.java:265)
    at org.springframework.test.web.reactive.server.DefaultWebTestClient.mutateWith(DefaultWebTestClient.java:167)

As far as I have understood it, this WebTestClient setup is only suitable for "Reactive Applications" whereas my application is a "Servlet Application". Unfortunately, I cannot find the necessary information how to mock this OAuth2 client for a servlet application.

Answer 1

I was able to run your exact @Autowired and @Test code successfully with the following test configuration:

@Configuration
@ComponentScan
public class TestConfig {

    @Bean
    public WebTestClient webTestClient(ApplicationContext applicationContext) {
        return WebTestClient.bindToApplicationContext(applicationContext).build();
    }

    @Bean
    public SecurityWebFilterChain securityFilterChain(ServerHttpSecurity http) {
        http.authorizeExchange().anyExchange().permitAll();
        return http.build();
    }
}