code: @Override
    protected void additionalAuthenticationChecks(UserDetails userDetails,
        UsernamePasswordAuthenticationToken authentication) throws AuthenticationException {
  
      // default implementation authentications via servlet API (container managed)
      ServletRequestAttributes currentRequestAttributes =
          (ServletRequestAttributes) RequestContextHolder.currentRequestAttributes();
  
      HttpServletRequest request = currentRequestAttributes.getRequest();
      String login = authentication.getName();
      String password = null;
      Object credentials = authentication.getCredentials();
      if (credentials != null) {
        password = credentials.toString();
      }
      try {
        request.login(login, password);
      } catch (ServletException e) {
        LOG.warn("Authentication failed: {}", e.toString());
        throw new BadCredentialsException("Authentication failed.", e);
      }
      authentication.setDetails(userDetails);
    }
docs: Here the actual authentication has to be implemented.<br/>
  <br/>