根据 id 生成唯一短字符串（防止用户 id 等暴露), 用 hashids 稳妥不？

[kkk212]

https://hashids.org/
Hashids is a small open-source library that generates short, unique, non-sequential ids from numbers.

It converts numbers like 347 into strings like “ yr8 ”, or array of numbers like [27, 986] into “ 3kTMd ”.

You can also decode those ids back. This is useful in bundling several parameters into one or simply using them as short UIDs.

比如字符串长度设置 4-6 位，等用户量大了接近 4-6 位字符能表示的用户量时, 会不会出现重复的。

[jifengg]

如果区分大小写，26 个字母+10 个数字，6 位可以有 (26+26+10)^6=56800235584，568 亿个不重复的字符串。
但是位数少了有一个问题就是重复率会增加，需要排重的时间会增加。可以的情况下，位数尽可能多一些。

[trowa8509]

用 JWT 吧。