@SukkaW review please

I myself don't like the idea of pre-exists certificate.

vercel/next.js#54016

What about using mkcert of some sort?

mkcert same as openssl the function is same (making locally-trusted self-certificate). user can define their own certificate by passing --cert and --key on hexo server cli

Agreed, pre-exists certificate may be difficult to trust

Agreed, pre-exists certificate may be difficult to trust

Then, what is the solution? Should auto certificate creation be made?
If there is no localhost or 127.0.0.1 certificate then you cannot use SSL for localhost.

Btw, this feature no need user to install the certificate into their computer. This certificate only for NodeJS http server.
This only uses for outgoing http connection to target url which have SSL with strict rule (cannot mixed incoming connection from http like localhost).

So, this feature does not harm its users.
Useful for adsense localhost testing.
Useful for develop Hexo theme with adsense or other ads platform feature (banner, interstitial, video ads).

Then, what is the solution? Should auto certificate creation be made?

At least the certificate should be generated per hexo project and on users' computers. We can store the generated certificates under the node_modules/.cache/hexo-server-certificates folder.

You can refer to vercel/next.js#54016 for the implementation. They are utilizing mkcert to generate a certificate on users' computers per the Next.js project. Unlike OpenSSL, mkcert is a single statically linked binary that can run almost anywhere.

So, this feature does not harm its users.

This is just not even remotely a good practice. Let's avoid it.