title: Spring Boot AuthenticationFilterConfiguration.onStartup is not called
body: <p>I have the following configuration class:</p>
  
  <pre><code>@Configuration
  public class AuthenticationFilterConfiguration extends SpringBootServletInitializer {
  
      private static final Logger LOGGER = LoggerFactory.getLogger(AuthenticationFilterConfiguration.class);
  
      public AuthenticationFilterConfiguration(){
          LOGGER.info("Setting up authentication filter");
      }
  
      @Override
      public void onStartup(ServletContext context) throws ServletException {
          super.onStartup(context);
          LOGGER.info("Authentication filter configured");
      }
  
  }
  </code></pre>
  
  <p>This is in the same package as the main application:</p>
  
  <pre><code>@SpringBootApplication
  public class MainApplication {
      public static void main(String[] args) {
          SpringApplication.run(MainApplication.class, args);
      }
  }
  </code></pre>
  
  <p>In my log - I see:</p>
  
  <blockquote>
    <blockquote>
      <p>2018-04-10 AuthenticationFilterConfiguration  : Setting up authentication filter</p>
    </blockquote>
  </blockquote>
  
  <p>However, I never see the log message from the <code>onStartup(...)</code> method that says <code>Authentication filter configured</code>.  My other <code>@Configuration</code> classes are being loaded (they have lots of <code>@Bean</code>s that they create)</p>
  
  <p>Why is the onStartup method not being called?  Everything else works, my RESTful endpoints are working, etc...</p>