code: @Override
      public void init(FilterConfig filterConfig) throws ServletException {
          LOG.info("AtlasAuthenticationFilter initialization started");
          final FilterConfig globalConf = filterConfig;
          final Map<String, String> params = new HashMap<>();
          try {
              configuration = ApplicationProperties.get();
          } catch (Exception e) {
              throw new ServletException(e);
          }
  
          if (configuration != null) {
              headerProperties = ConfigurationConverter.getProperties(configuration.subset("atlas.headers"));
          }
  
          FilterConfig filterConfig1 = new FilterConfig() {
              @Override
              public ServletContext getServletContext() {
                  if (globalConf != null) {
                      return globalConf.getServletContext();
                  } else {
                      return nullContext;
                  }
              }
  
              @SuppressWarnings("unchecked")
              @Override
              public Enumeration<String> getInitParameterNames() {
                  return new IteratorEnumeration(params.keySet().iterator());
              }
  
              @Override
              public String getInitParameter(String param) {
                  return params.get(param);
              }
  
              @Override
              public String getFilterName() {
                  return "AtlasAuthenticationFilter";
              }
          };
  
          super.init(filterConfig1);
  
          optionsServlet = new HttpServlet() {
          };
          optionsServlet.init();
      }
docs: Initialize the filter.
  
  @param filterConfig filter configuration.
  @throws ServletException thrown if the filter could not be initialized.