NewCertificate sets up everything needed for Lego to move forward with cert issuance and renewal, as well as generating a unique ID, and a cryptographically secure secret.

NewUser creates a user object with a hashed version of the passed in password.

ValidDomains is used to validate that the passed domains set includes only valid domains (ie example.com or *.example.com).

DefaultRenewAt is the number of days before expiration a cert should be renewed at.

ChallengeConfig provides all necessary information for a Cloudflare DNS Challenge provider.

Config holds all the necessary application level configuration items.

User is a system user for the webapp.