CFSSL
Cloudflare's PKI and TLS toolkit
...Users of these distributions should install go manually to install CFSSL. You can set the GOOS and GOARCH environment variables to have Go cross compile for alternative platforms; however, cfssl requires cgo, and cgo requires a working compiler toolchain for the target platform. The csr is the client's certificate request. The -ca and -ca-key flags are the CA's certificate and private key, respectively. By default, they are ca.pem and ca_key.pem. The -hostname is a comma separated hostname list that overrides the DNS names and IP address in the certificate SAN extension.