Add authentication to the site

[CaliCastle]

I think I should add authentication to the site because it'll be easier for people to interact with it and actually persist interaction data from other users.

Clerk sounds like an interesting option recently, might need to look into it.
Other available options:

• Auth0
• Custom solution (would need NextAuth for sure)

[Alex20180512]

（不能完全 get 到，英文是一坨 shit）这个 issue 的意思是不是想接一个类似谷歌登录的功能进来？但我又感觉像是想接 Google reCAPTCHA？