Let’s Encrypt client and ACME library written in Go.
Features

• ACME v2 [RFC 8555}(https://www.rfc-editor.org/rfc/rfc8555.html)
• Register with CA
• Obtain certificates, both from scratch or with an existing CSR
• Renew certificates
• Revoke certificates
• Robust implementation of all ACME challenges
  • HTTP (http-01)
  • DNS (dns-01)
  • TLS (tls-alpn-01)
• SAN certificate support
• Comes with multiple optional DNS providers
• Custom challenge solvers
• Certificate bundling
• OCSP helper function

github: LEGO