code: public UserDetails loadUserByUsername(String username)
          throws UsernameNotFoundException {
          UserDetails userDetails = usersTable.get(username);
          if (null == userDetails) {
              throw new UsernameNotFoundException(username);
          }
          return userDetails;
      }
docs: This method retrieves UserDetails for all users from a flat file in
  DuraCloud.
  
  @param username of principal for whom details are sought
  @return UserDetails for arg username
  @throws UsernameNotFoundException if username not found