JHipster API Gateway - Microservices Endpoints Missing in Swagger Spring Boot 3.3.5

Question

JHipster API Gateway - Microservices Endpoints Missing in Swagger After Spring Boot 3.3.5 Upgrade

I have a JHipster API Gateway where Swagger (http://localhost:8080/admin/api-docs) does not display the endpoints of other microservices after upgrading to Spring Boot 3.3.5.

Environment

JHipster: 8.7.3
Spring Boot: 3.3.5
Spring Cloud: 2023.0.3
WebFlux on Gateway
Spring MVC on Microservices

After upgrading to Spring Boot 3.3.5 (which includes WebFlux 6.1.14), the issue appears. However, in Spring Boot 3.3.4 (WebFlux 6.1.13), everything works fine.

Observations

The ModifyServersOpenApiFilter is supposed to intercept API docs requests, but logs indicate it is not being executed in 3.3.5.
A JWT decoder (JwtDecoder) is never invoked when debugging in 3.3.5, but it works fine in 3.3.4.
Microservices return 500 Internal Server Error when requested via the gateway.
Logs from Spring Boot 3.3.4 (missing in 3.3.5) show JWT authentication being applied to api-docs requests, meaning security might be blocking the API documentation retrieval.

Example Code

ModifyServersOpenApiFilter

This should intercept and modify API Docs responses:

public class ModifyServersOpenApiFilter implements GlobalFilter, Ordered {
    private static final String OPEN_API_PATH = "/v3/api-docs";
    private static final Logger log = LoggerFactory.getLogger(ModifyServersOpenApiFilter.class);

    @Override
    public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        String path = exchange.getRequest().getURI().getRawPath();
        log.info("DEBUG PATH in ModifyServersOpenApiFilter: {}", path);

        if (path.startsWith("/services") && path.contains(OPEN_API_PATH)) {
            ServerHttpResponse originalResponse = exchange.getResponse();
            DataBufferFactory bufferFactory = originalResponse.bufferFactory();
            ServerHttpResponseDecorator decoratedResponse = createModifyServersOpenApiInterceptor(path, originalResponse, bufferFactory);
            log.info("AUTH HEADER: {}", exchange.getRequest().getHeaders().get("Authorization"));

            return chain.filter(exchange.mutate().response(decoratedResponse).build());
        } else {
            log.info("AUTH HEADER: {}", exchange.getRequest().getHeaders().get("Authorization"));
            return chain.filter(exchange);
        }
    }
}

JWT Decoder (Not Triggered in 3.3.5)

This is the JWT Decoder that works in Spring Boot 3.3.4 but is never executed in 3.3.5:

@Bean
JwtDecoder jwtDecoder() {
    NimbusJwtDecoder jwtDecoder = JwtDecoders.fromOidcIssuerLocation(issuerUri);

    OAuth2TokenValidator audienceValidator = new AudienceValidator(jHipsterProperties.getSecurity().getOauth2().getAudience());
    OAuth2TokenValidator withIssuer = JwtValidators.createDefaultWithIssuer(issuerUri);
    OAuth2TokenValidator withAudience = new DelegatingOAuth2TokenValidator<>(withIssuer, audienceValidator);

    jwtDecoder.setJwtValidator(withAudience);
    return jwtDecoder;
}

Possible Cause

The behavior in Spring Boot 3.3.5 is similar to this reported issue.

It seems that the upgrade may have introduced a blocking thread issue with WebFlux that prevents API documentation requests from being properly processed.

Questions

Is there a known issue with Spring Boot 3.3.5 + WebFlux 6.1.14 that affects JHipster Gateway's ability to retrieve API Docs?
Could this be related to security filters or JWT authentication blocking requests?
Any workaround for this issue, other than downgrading to Spring Boot 3.3.4?

What I Tried and Expected

Downgrading Spring Boot: I downgraded from Spring Boot 3.3.5 to 3.3.4, and the problem was resolved. This indicates that something introduced in 3.3.5 is causing the issue.
Changing JWT Decoders: I tried modifying the JwtDecoder configuration, but it had no effect. The JWT decoder is not being triggered at all in Spring Boot 3.3.5, while it works fine in 3.3.4.
Checking Logs: In 3.3.4, logs show authentication steps and API documentation requests being processed correctly. In 3.3.5, these logs are missing, and microservices return a 500 Internal Server Error instead.

Expected Behavior

Swagger should display all microservice endpoints correctly in the API Gateway (/admin/api-docs). JWT authentication should function as expected, allowing secure access to API documentation.

Actual Result

Swagger does not display microservice endpoints in the Gateway.
JWT decoder is never triggered in 3.3.5, while it works in 3.3.4.
Microservices return 500 Internal Server Error when accessed via the API Gateway.

Api gateway network log

Example Logs on Service (Spring Boot 3.3.4)

In Spring Boot 3.3.4, logs show successful service discovery, authentication, and secured requests:

2025-02-28T16:31:40.023+03:00  INFO 15948 --- [foReplicator-%d] com.netflix.discovery.DiscoveryClient    : Saw local status change event StatusChangeEvent [timestamp=1740749500023, current=UP, previous=DOWN] 
2025-02-28T16:31:40.023+03:00  INFO 15948 --- [foReplicator-%d] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_WORKFLOW SERVICE/workflow service:bfd4a39b6c2133c10ff13f994de905ca: registering service... 
2025-02-28T16:31:40.039+03:00  INFO 15948 --- [foReplicator-%d] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_WORKFLOW SERVICE/workflow service:bfd4a39b6c2133c10ff13f994de905ca - registration status: 204 
2025-02-28T16:32:00.002+03:00  INFO 15948 --- [ce-scheduling-1] c.s.w.s.workflow.WorkflowManagerService  : Lifetime check is running for the priority queue items.. 
2025-02-28T16:32:00.018+03:00  INFO 15948 --- [ce-scheduling-1] c.s.w.s.workflow.WorkflowManagerService  : Found 0 priority queue items to stop. 
2025-02-28T16:32:37.640+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.security.web.FilterChainProxy        : Securing GET /management/jhiopenapigroups 
2025-02-28T16:32:40.187+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.s.o.s.r.a.JwtAuthenticationProvider  : Authenticated token 
2025-02-28T16:32:40.189+03:00 DEBUG 15948 --- [  XNIO-1 task-2] .s.r.w.a.BearerTokenAuthenticationFilter : Set SecurityContextHolder to JwtAuthenticationToken [Principal=org.springframework.security.oauth2.jwt.Jwt@546d2b41, Credentials=[PROTECTED], Authenticated=true, Details=WebAuthenticationDetails [RemoteIpAddress=192.168.1.23, SessionId=null], Granted Authorities=[ROLE_ADMIN]] 
2025-02-28T16:32:40.199+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.security.web.FilterChainProxy        : Secured GET /management/jhiopenapigroups 
2025-02-28T16:33:00.005+03:00  INFO 15948 --- [ce-scheduling-2] c.s.w.s.workflow.WorkflowManagerService  : Lifetime check is running for the priority queue items.. 
2025-02-28T16:33:00.008+03:00  INFO 15948 --- [ce-scheduling-2] c.s.w.s.workflow.WorkflowManagerService  : Found 0 priority queue items to stop. 
2025-02-28T16:34:00.002+03:00  INFO 15948 --- [ce-scheduling-2] c.s.w.s.workflow.WorkflowManagerService  : Lifetime check is running for the priority queue items.. 
2025-02-28T16:34:00.007+03:00  INFO 15948 --- [ce-scheduling-2] c.s.w.s.workflow.WorkflowManagerService  : Found 0 priority queue items to stop. 
2025-02-28T16:34:01.645+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.security.web.FilterChainProxy        : Securing GET /v3/api-docs/springdocDefault 
2025-02-28T16:34:03.943+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.s.o.s.r.a.JwtAuthenticationProvider  : Authenticated token 
2025-02-28T16:34:03.944+03:00 DEBUG 15948 --- [  XNIO-1 task-2] .s.r.w.a.BearerTokenAuthenticationFilter : Set SecurityContextHolder to JwtAuthenticationToken [Principal=org.springframework.security.oauth2.jwt.Jwt@546d2b41, Credentials=[PROTECTED], Authenticated=true, Details=WebAuthenticationDetails [RemoteIpAddress=192.168.1.23, SessionId=null], Granted Authorities=[ROLE_ADMIN]] 
2025-02-28T16:34:03.946+03:00 DEBUG 15948 --- [  XNIO-1 task-2] o.s.security.web.FilterChainProxy        : Secured GET /v3/api-docs/springdocDefault 
2025-02-28T16:34:04.533+03:00  INFO 15948 --- [  XNIO-1 task-2] o.springdoc.api.AbstractOpenApiResource  : Init duration for springdoc-openapi is: 572 ms