go get: installing executables with 'go get' in module mode is deprecated.

[SandMouse]

While running step 7 of your instructions: sudo ./setup_cfssl.sh I encounter:

go get: installing executables with 'go get' in module mode is deprecated.
	Use 'go install pkg@version' instead.
	For more information, see https://golang.org/doc/go-get-install-deprecation
	or run 'go help get' or 'go help install'.

[Paper-Dragon]

You mast install low version go execute, I having install go's version is 1.16

[Felix273]

Replace the go get commands with

go install bitbucket.org/liamstask/goose/cmd/goose@latest
go install github.com/cloudflare/cfssl/cmd/cfssl@latest