Thymeleaf tags for Spring Security

add thymeleaf XML namespace to index.html

https://github.com/thymeleaf/thymeleaf-extras-springsecurity
Thymeleaf Extras

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:th="http://www.thymeleaf.org"
      xmlns:sec="http://www.thymeleaf.org/extras/spring-security">

<div sec:authorize="hasRole('ADMIN')">
    This content is only shown to administrators.§§
</div>

<div sec:authorize="hasRole('USER')">
    This content is only shown to users.
    Content is not just hidden from view but will not be rendered when our application server returns the page to the browser.
</div>

    retrieve the user's username and roles and display these in our HTML
    <div>
    User: <span sec:authentication="name">NOT FOUND</span>
    Spring Roles: <span sec:authentication="principal.authorities">NOT FOUND</span>
</div>