Spring Security: Set GrantedAuthorities

you can do it with following code:

Collection<SimpleGrantedAuthority> oldAuthorities = (Collection<SimpleGrantedAuthority>)SecurityContextHolder.getContext().getAuthentication().getAuthorities();
SimpleGrantedAuthority authority = new SimpleGrantedAuthority("ROLE_ANOTHER");
List<SimpleGrantedAuthority> updatedAuthorities = new ArrayList<SimpleGrantedAuthority>();
updatedAuthorities.add(authority);
updatedAuthorities.addAll(oldAuthorities);

SecurityContextHolder.getContext().setAuthentication(
        new UsernamePasswordAuthenticationToken(
                SecurityContextHolder.getContext().getAuthentication().getPrincipal(),
                SecurityContextHolder.getContext().getAuthentication().getCredentials(),
                updatedAuthorities)
);