Lego Let’s Encrypt client and ACME library written in Go. Features ACME v2 RFC 8555 Support RFC 8737: TLS Application‑Layer Protocol Negotiation (ALPN) Challenge Extension Support RFC 8738: issues certificates for IP addresses Support draft-ietf-acme-ari-01: Renewal Information (ARI) Extension Register with CA Obtain certificates, both from scratch or with an existing CSR Renew certificates Revoke