I have an application in Spring Boot released on Cloud Run with IAP authentication. If I text locally I get this error:

java.lang.NullPointerException: Cannot invoke “org.springframework.security.core.Authentication.getName()” because “authentication” is null
at com.wind.cbrweb.web.HomeController.handleRequest(HomeController.java:56) ~[classes/:0.0.1-SNAPSHOT]

I’m using this library:

<dependency>
            <groupId>com.google.cloud</groupId>
            <artifactId>spring-cloud-gcp-starter-security-iap</artifactId>
 </dependency>

my Security Context class:

@Configuration
@EnableWebSecurity
public class SecurityConfiguration {
    
    protected final Log logger = LogFactory.getLog(getClass());  
    
      @Bean
      public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests((authorizeHttpRequests) ->
                    authorizeHttpRequests
                    .requestMatchers("/**").permitAll().anyRequest().authenticated())
        .oauth2ResourceServer(oauth2 -> oauth2.jwt(Customizer.withDefaults()));
        
       http.headers((headers) -> headers
           .frameOptions((frameOptions) -> frameOptions.disable()));

        return http.build();
      }
    
}

my application properties file:

spring.cloud.gcp.security.iap.registry=https://www.gstatic.com/iap/verify/public_key-jwk
spring.cloud.gcp.security.iap.algorithm=ES256
spring.cloud.gcp.security.iap.header=x-goog-iap-jwt-assertion
spring.cloud.gcp.security.iap.issuer=https://cloud.google.com/iap
spring.cloud.gcp.security.iap.audience=/projects/PROJECT_ID/global/backendServices/SERVICE_ID

this is the controller of the first page after IAP authentication:

@Controller
public class HomeController {
    protected final Log logger = LogFactory.getLog(getClass());
    
    @Autowired
    private UserManager userManager;
    
    @Autowired
    private Firestore firestore;
    
    @GetMapping("/")
    public String redirectToHome(Authentication authentication) {

        return "redirect:/home.htm";
    }

    @GetMapping("/home.htm")
    public ModelAndView handleRequest(HttpServletRequest req,
            HttpServletResponse res, Authentication authentication) throws Exception {
        logger.info("Returning home view");
        
                String currentUserName = authentication.getName();
        
        //OTHER CODE
    }
}

How can I create a user to simulate Google IAP authentication? I expect that when I run the Spring /home application I have Authentication filled with the Principal information (group to which I belong, name, user_id, etc.). Then simulate the authentication as on IAP