ACME Protocol (RFC 8555)

Automatic Certificate Management Environment — an IETF standard protocol (RFC 8555) that enables fully automated certificate issuance, renewal, and revocation between clients and certificate authorities. An ACME client proves domain control by completing challenges: HTTP-01 (serve a file at a well-known URL), DNS-01 (add a TXT record), or TLS-ALPN-01 (respond to a TLS connection). ACME eliminates manual CSR submission and certificate installation workflows. Popular ACME clients include Certbot, acme.sh, win-acme, and the built-in clients in Caddy and Traefik.