code: public static final AccessControlListHandler acl(final HttpHandler next, boolean defaultAllow, ExchangeAttribute attribute) {
          return new AccessControlListHandler(next, attribute).setDefaultAllow(defaultAllow);
      }
docs: Returns a new handler that can allow or deny access to a resource based an at attribute of the exchange
  
  @param next         The next handler in the chain
  @param defaultAllow Determine if a non-matching user agent will be allowed by default
  @return A new user agent access control handler