什么是单点登录(SSO)

/**
 * 用户登陆
 */
@PostMapping(value = "/user/session", produces = {"application/json;charset=UTF-8"})
public Result login(String mobileNo, String password, String inputCaptcha, HttpSession session, HttpServletResponse response) {
    //判断验证码是否正确
    if (WebUtils.validateCaptcha(inputCaptcha, "captcha", session)) {
        //判断有没有该用户
        User user = userService.userLogin(mobileNo, password);
        if (user != null) {
            /*设置自动登陆，一个星期.  将token保存在数据库中*/
            String loginToken = WebUtils.md5(new Date().toString() + session.getId());
            user.setLoginToken(loginToken);
            User user1 = userService.userUpload(user);
            session.setAttribute("user", user1);
            CookieUtil.addCookie(response,"loginToken",loginToken,604800);
            return ResultUtil.success(user1);
        } else {
            return ResultUtil.error(ResultEnum.LOGIN_ERROR);
        }
    } else {
        return ResultUtil.error(ResultEnum.CAPTCHA_ERROR);
    }
}
/**
 * 用户退出
 */
@DeleteMapping(value = "/session", produces = {"application/json;charset=UTF-8"})
public Result logout(HttpSession session,HttpServletRequest request,HttpServletResponse response ) {
    //删除session和cookie
    session.removeAttribute("user");
    CookieUtil.clearCookie(request, response, "loginToken");
    return ResultUtil.success();
}
/**
* @author ozc
* @version 1.0
* <p>
* 拦截器；实现自动登陆功能
*/
public class UserInterceptor implements HandlerInterceptor {
@Autowired
private UserService userService;
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object o) throws Exception {
    User sessionUser = (User) request.getSession().getAttribute("user");
    // 已经登陆了，放行
    if (sessionUser != null) {
        return true;
    } else {
        //得到带过来cookie是否存在
        String loginToken = CookieUtil.findCookieByName(request, "loginToken");
        if (StringUtils.isNotBlank(loginToken)) {
            //到数据库查询有没有该Cookie
            User user = userService.findUserByLoginToken(loginToken);
            if (user != null) {
                request.getSession().setAttribute("user", user);
                return true;
            } else {
                //没有该Cookie与之对应的用户(Cookie不匹配)
                CookieUtil.clearCookie(request, response, "loginToken");
                return false;
            }
        } else {
            //没有cookie、也没有登陆。是index请求获取用户信息，可以放行
            if (request.getRequestURI().contains("session")) {
                return true;
            }
            //没有cookie凭证
            response.sendRedirect("/login.html");
            return false;
        }
    }
}
}

// 登录功能(SSO单独的服务)
@Override
public TaotaoResult login(String username, String password) throws Exception {
    //根据用户名查询用户信息
    TbUserExample example = new TbUserExample();
    Criteria criteria = example.createCriteria();
    criteria.andUsernameEqualTo(username);
    List<TbUser> list = userMapper.selectByExample(example);
    if (null == list || list.isEmpty()) {
        return TaotaoResult.build(400, "用户不存在");
    }
    //核对密码
    TbUser user = list.get(0);
    if (!DigestUtils.md5DigestAsHex(password.getBytes()).equals(user.getPassword())) {
        return TaotaoResult.build(400, "密码错误");
    }
    //登录成功，把用户信息写入redis
    //生成一个用户token
    String token = UUID.randomUUID().toString();
    jedisCluster.set(USER_TOKEN_KEY + ":" + token, JsonUtils.objectToJson(user));
    //设置session过期时间
    jedisCluster.expire(USER_TOKEN_KEY + ":" + token, SESSION_EXPIRE_TIME);
    return TaotaoResult.ok(token);
}

public TaotaoResult login(String username, String password, 
        HttpServletRequest request, HttpServletResponse response) {
    //请求参数
    Map<String, String> param = new HashMap<>();
    param.put("username", username);
    param.put("password", password);
    //登录处理
    String stringResult = HttpClientUtil.doPost(REGISTER_USER_URL + USER_LOGIN_URL, param);
    TaotaoResult result = TaotaoResult.format(stringResult);
    //登录出错
    if (result.getStatus() != 200) {
        return result;
    }
    //登录成功后把取token信息，并写入cookie
    String token = (String) result.getData();
    //写入cookie
    CookieUtils.setCookie(request, response, "TT_TOKEN", token);
    //返回成功
    return result;
}