Spring 4.3.6 STOMP / WebSockets with auth-token

SOLVED: see comment

I am currently trying to open a WebSockets connection between a spring server and an angular client with a x-auth-token. Therefore I have the following pieces of code:

import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.messaging.simp.config.ChannelRegistration;
import org.springframework.messaging.support.ChannelInterceptorAdapter;
import org.springframework.messaging.support.MessageHeaderAccessor;
import org.springframework.messaging.Message; 
import org.springframework.messaging.MessageChannel; 
import org.springframework.messaging.simp.stomp.StompCommand;
import org.springframework.messaging.simp.stomp.StompSession;
import org.springframework.messaging.simp.stomp.StompHeaders;
import org.springframework.messaging.simp.stomp.StompHeaderAccessor; 
import org.springframework.web.socket.config.annotation.AbstractWebSocketMessageBrokerConfigurer;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Configuration
@EnableWebSocketMessageBroker
@Order(Ordered.HIGHEST_PRECEDENCE + 99)
public class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {

    private final Logger LOGGER = LoggerFactory.getLogger(this.getClass());

    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/topic");
        config.setApplicationDestinationPrefixes("/app");
    }

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        LOGGER.info("registering websockets");
        registry.addEndpoint("/api/v1/websocket").setAllowedOrigins("*").withSockJS();
    }

    @Override
    public void handleException(StompSession session, StompCommand command, StompHeaders headers, byte[] payload, Throwable exceptio) {
        LOGGER.info("ERRORORRRRRRRR");
        exception.printStackTrace();
    }

    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
      registration.setInterceptors(new ChannelInterceptorAdapter() {

          @Override
          public Message<?> preSend(Message<?> message, MessageChannel channel) {

              StompHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, StompHeaderAccessor.class);

              LOGGER.info("in override");

              if (StompCommand.CONNECT.equals(accessor.getCommand())) {

                  String authToken = accessor.getFirstNativeHeader("x-auth-token");

                  LOGGER.info("Header auth token: " + authToken);

                  // Principal user = ... ; // access authentication header(s)
                  //accessor.setUser(user);
              }

              return message;
          }
      });
    }
}

As you can see from my WebSocketConfig I am currently not really processing the x-auth-token, but rather trying to log it once. In the end I was trying to follow the Spring documentation: https://docs.spring.io/spring/docs/current/spring-framework-reference/html/websocket.html#websocket-stomp-authentication-token-based

The only problem I have with this is that in configureClientInboundChannel() the preSend() method seems not get called - and I cannot figure out why.

On the client side, the following error is displayed:

As you can see by comparing the error log and the endpoint defined in registerStompEndpoints() shows the actual endpoint is the correct one. Still I do not understand, why LOGGER.info("in override"); in configureClientInboundChannel() is not called.

I would really like to go with the auth-token being transferred via the stomp headers instead of the hacky token-as-URL-paramter-solution. Does someone here have an idea? Did I miss something in the already linked spring documentation?

Thanks in advance for your help!