// HTTP01 is the "http-01" ACME challenge https://github.com/ietf-wg-acme/acme/blob/master/draft-ietf-acme-acme.md#http
// Note: HTTP01ChallengePath returns the URL path to fulfill this challenge
HTTP01=Challenge("http-01")
// TLSSNI01 is the "tls-sni-01" ACME challenge https://github.com/ietf-wg-acme/acme/blob/master/draft-ietf-acme-acme.md#tls-with-server-name-indication-tls-sni
// Note: TLSSNI01ChallengeCert returns a certificate to fulfill this challenge
TLSSNI01=Challenge("tls-sni-01")
// DNS01 is the "dns-01" ACME challenge https://github.com/ietf-wg-acme/acme/blob/master/draft-ietf-acme-acme.md#dns
// Note: DNS01Record returns a DNS record which will fulfill this challenge