code: public void start()
          throws Exception
      {
          if (getHttpContext().getAuthenticator()==null)
          {
              // Find out the Authenticator.
              if (SecurityConstraint.__BASIC_AUTH.equalsIgnoreCase(_authMethod))
                  getHttpContext().setAuthenticator(new BasicAuthenticator());
              else if (SecurityConstraint.__CERT_AUTH.equalsIgnoreCase(_authMethod))
                  getHttpContext().setAuthenticator(new ClientCertAuthenticator());
              else
                  log.warn("Unknown Authentication method:"+_authMethod);
          }
          
          super.start();
      }
docs: /* ------------------------------------------------------------