const (
    StatusUnknown    = "unknown"
    StatusPending    = "pending"
    StatusProcessing = "processing"
    StatusValid      = "valid"
    StatusInvalid    = "invalid"
    StatusRevoked    = "revoked"
)

type Account struct {
    // URI is the account unique ID, which is also a URL used to retrieve
    // account data from the CA.
    URI string

    // Contact is a slice of contact info used during registration.
    Contact []string

    // The terms user has agreed to.
    // Zero value indicates that the user hasn't agreed yet.
    AgreedTerms string

    // Actual terms of a CA.
    CurrentTerms string

    // Authz is the authorization URL used to initiate a new authz flow.
    Authz string

    // Authorizations is a URI from which a list of authorizations
    // granted to this account can be fetched via a GET request.
    Authorizations string

    // Certificates is a URI from which a list of certificates
    // issued for this account can be fetched via a GET request.
    Certificates string
}

type Authorization struct {
    // URI uniquely identifies a authorization.
    URI string

    // Status identifies the status of an authorization.
    Status string

    // Identifier is what the account is authorized to represent.
    Identifier AuthzID

    // Challenges that the client needs to fulfill in order to prove possession
    // of the identifier (for pending authorizations).
    // For final authorizations, the challenges that were used.
    Challenges []*Challenge

    // A collection of sets of challenges, each of which would be sufficient
    // to prove possession of the identifier.
    // Clients must complete a set of challenges that covers at least one set.
    // Challenges are identified by their indices in the challenges array.
    // If this field is empty, the client needs to complete all challenges.
    Combinations [][]int
}

type AuthzID struct {
    Type  string // The type of identifier, e.g. "dns".
    Value string // The identifier itself, e.g. "example.org".
}

type Challenge struct {
    // Type is the challenge type, e.g. "http-01", "tls-sni-02", "dns-01".
    Type string

    // URI is where a challenge response can be posted to.
    URI string

    // Token is a random value that uniquely identifies the challenge.
    Token string

    // Status identifies the status of this challenge.
    Status string
}

type Client struct {
    // HTTPClient optionally specifies an HTTP client to use
    // instead of http.DefaultClient.
    HTTPClient *http.Client

    // Key is the account key used to register with a CA
    // and sign requests.
    Key *rsa.PrivateKey
}

type Directory struct {
    // RegURL is an account endpoint URL, allowing for creating new
    // and modifying existing accounts.
    RegURL string

    // AuthzURL is used to initiate Identifier Authorization flow.
    AuthzURL string

    // CertURL is a new certificate issuance endpoint URL.
    CertURL string

    // RevokeURL is used to initiate a certificate revocation flow.
    RevokeURL string

    // Term is a URI identifying the current terms of service.
    Terms string

    // Website is an HTTP or HTTPS URL locating a website
    // providing more information about the ACME server.
    Website string

    // CAA consists of lowercase hostname elements, which the ACME server
    // recognises as referring to itself for the purposes of CAA record validation
    // as defined in RFC6844.
    CAA []string
}

type Error struct {
    // StatusCode is The HTTP status code generated by the origin server.
    StatusCode int
    // ProblemType is a URI reference that identifies the problem type,
    // typically in a "urn:acme:error:xxx" form.
    ProblemType string
    // Detail is a human-readable explanation specific to this occurrence of the problem.
    Detail string
    // Header is the original server error response headers.
    Header http.Header
}