@Override
    public Authorizer<T> orElse(Authorizer<T> nextAuthorizer) {
        final ImmutableList.Builder<Authorizer<T>> newAuthorizersBuilder = ImmutableList.builder();
        newAuthorizersBuilder.addAll(authorizers);
        requireNonNull(nextAuthorizer, "nextAuthorizer");
        if (nextAuthorizer instanceof AuthorizerChain) {
            newAuthorizersBuilder.addAll(((AuthorizerChain<T>) nextAuthorizer).authorizers);
        } else {
            newAuthorizersBuilder.add(nextAuthorizer);
        }
        return new AuthorizerChain<T>(newAuthorizersBuilder.build(), selectionStrategy);
    }
Adds a new {@link Authorizer} to the chain.
@return an original {@link AuthorizerChain} instance with added {@link Authorizer}.
core/src/main/java/com/linecorp/armeria/server/auth/AuthorizerChain.java