code: private void authorizer(final Object authorizer, final String name, final String pattern) {
      requireNonNull(name, "An authorizer's name is required.");
      requireNonNull(pattern, "An authorizer's pattern is required.");
      requireNonNull(authorizer, "An authorizer is required.");
      authorizers.put(pattern, Maps.immutableEntry(name, authorizer));
    }
docs: Protect one or more urls with an {@link Authorizer}. For example:
  <pre>
  {
  use(new Auth()
  .form("*")
  .authorizer("admin", "/admin/**", MyAuthorizer.class)
  );
  }
  </pre>
  <p>
  Previous example will protect any url with form authentication and require and admin role for
  <code>/admin/</code> or subpath of it.
  </p>
  
  @param name Authorizer name.
  @param pattern URL pattern to protected.
  @param authorizer Authorizer to apply.