Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();
    String username="tt";
    if (principal instanceof UserDetails) {
     username = ((UserDetails)principal).getUsername();
    } else {
     username = principal.toString();
    }
   return username;

@Configuration

/**In Memory Authentication
     * @param authenticationManagerBuilder Allow to build an AuthenticationManager
     */

     @Bean
public UserDetailsService mongoUserDetails() {
    return new UserService();
}

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder authenticationManagerBuilder) {
        try {


           UserDetailsService userDetailsService = mongoUserDetails();
            authenticationManagerBuilder.userDetailsService(userDetailsService);

        } catch (Exception exception) {

            LOG.error("In Memory Authentication has failed", exception);
        }


    }

@Service

@Override
public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    MongoCollection<Document> collection = MongoConnection.getConnection().getCollection("users");
    Document document = collection.find(Filters.eq("username",username)).first();
    if(document!=null) {
        String username1 = document.getString("username");
        String password = document.getString("password");
        List<String> authorities = (List<String>) document.get("authorities");
        MongoUserDetails mongoUserDetails = new MongoUserDetails(username1,password,authorities.toArray(new String[authorities.size()]));
        return mongoUserDetails;
    }
    return null;
}