public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
      throws IOException, ServletException {

    HttpServletRequest request = (HttpServletRequest) servletRequest;
    HttpServletResponse response = (HttpServletResponse) servletResponse;

    String authHeader = request.getHeader("Authorization");
    if (Objects.isNonNull(authHeader)) {
      StringTokenizer st = new StringTokenizer(authHeader);
      if (st.hasMoreTokens()) {
        String basic = st.nextToken();

        if (basic.equalsIgnoreCase(BASIC)) {
          try {
            String credentials = new String(Base64.decodeBase64(st.nextToken()), UTF-
            int p = credentials.indexOf(DOUBLE_DOT);
            if (isValid(p)) {
              String username =  parseUsername(credentials);
              String password = parsePassword(credentials);

              if (!userService.checkUsername(username) || userService.checkPassword(password)) {
                unauthorized(response, "Bad credentials");
              }

              filterChain.doFilter(servletRequest, servletResponse);
            } else {
              unauthorized(response, "Invalid authentication token");
            }
          } catch (UnsupportedEncodingException e) {
            throw new AuthentificationException("Couldn't retrieve authentication", e);
          }
        }
      }
    } else {
      unauthorized(response);
    }
  }