server: automatically generate a self-signed certificate

[lonnywong]

Automatically generate a self-signed certificate if ssl is enabled and no certificate and key files are specified.

[lonnywong]

@tsl0922 Can you rerun the tests? All tests should succeed.

[morph027]

Oh, thank you, just tested this PR successully 🎉 😍

[tsl0922]

Why? I think it is outside the scope of this project.

I would recommend using tools like mkcert or cfssl if you don't like openssl cli in SSL Usage.

[lonnywong]

Why? I think it is outside the scope of this project.

I would recommend using tools like mkcert or cfssl if you don't like openssl cli in SSL Usage.

It will be much more convenient when you need to use https temporarily, without having to read the manual of other tools.

[tsl0922]

It introduces maintenance cost in this project, and I'm not a security expert on SSL, so it won't be merged here.