base64 由哪64个字符构成
Issue 欢迎在 Gtihub Issue 中回答此问题: Issue 303 (opens in a new tab)
Author 回答者: shfshanyue (opens in a new tab)
A-Z，a-z，0-9，+，/
Author 回答者: haotie1990 (opens in a new tab)
https://www.ruanyifeng.com/blog/2008/06/base64.html (opens in a new tab)