CFSSL is Cloudflare's PKI/TLS swiss army knife. It is both a command line tool
and an HTTP API server for signing, verifying, and bundling TLS certificates.

CFSSL consists of:
* a set of packages useful for building custom TLS PKI tools
* the cfssl program, which is the canonical command line utility using the
  CFSSL packages
* the multirootca program, which is a certificate authority server that can use
  multiple signing keys
* the mkbundle program is used to build certificate pool bundles
* the cfssljson program, which takes the JSON output from the cfssl and
  multirootca programs and writes certificates, keys, CSRs, and bundles to disk

WWW: https://cfssl.org/