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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package acme
import (
// ACME status values of Account, Order, Authorization and Challenge objects.
// See for details.
const (
StatusDeactivated = "deactivated"
StatusExpired = "expired"
StatusInvalid = "invalid"
StatusPending = "pending"
StatusProcessing = "processing"
StatusReady = "ready"
StatusRevoked = "revoked"
StatusUnknown = "unknown"
StatusValid = "valid"
// CRLReasonCode identifies the reason for a certificate revocation.
type CRLReasonCode int
// CRL reason codes as defined in RFC 5280.
const (
CRLReasonUnspecified CRLReasonCode = 0
CRLReasonKeyCompromise CRLReasonCode = 1
CRLReasonCACompromise CRLReasonCode = 2
CRLReasonAffiliationChanged CRLReasonCode = 3
CRLReasonSuperseded CRLReasonCode = 4
CRLReasonCessationOfOperation CRLReasonCode = 5
CRLReasonCertificateHold CRLReasonCode = 6
CRLReasonRemoveFromCRL CRLReasonCode = 8
CRLReasonPrivilegeWithdrawn CRLReasonCode = 9
CRLReasonAACompromise CRLReasonCode = 10
var (
// ErrUnsupportedKey is returned when an unsupported key type is encountered.
ErrUnsupportedKey = errors.New("acme: unknown key type; only RSA and ECDSA are supported")
// ErrAccountAlreadyExists indicates that the Client's key has already been registered
// with the CA. It is returned by Register method.
ErrAccountAlreadyExists = errors.New("acme: account already exists")
// ErrNoAccount indicates that the Client's key has not been registered with the CA.
ErrNoAccount = errors.New("acme: account does not exist")
// Error is an ACME error, defined in Problem Details for HTTP APIs doc
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
// Instance indicates a URL that the client should direct a human user to visit
// in order for instructions on how to agree to the updated Terms of Service.
// In such an event CA sets StatusCode to 403, ProblemType to
// "urn:ietf:params:acme:error:userActionRequired" and a Link header with relation
// "terms-of-service" containing the latest TOS URL.
Instance string
// Header is the original server error response headers.
// It may be nil.
Header http.Header
func (e *Error) Error() string {
return fmt.Sprintf("%d %s: %s", e.StatusCode, e.ProblemType, e.Detail)
// AuthorizationError indicates that an authorization for an identifier
// did not succeed.
// It contains all errors from Challenge items of the failed Authorization.
type AuthorizationError struct {
// URI uniquely identifies the failed Authorization.
URI string
// Identifier is an AuthzID.Value of the failed Authorization.
Identifier string
// Errors is a collection of non-nil error values of Challenge items
// of the failed Authorization.
Errors []error
func (a *AuthorizationError) Error() string {
e := make([]string, len(a.Errors))
for i, err := range a.Errors {
e[i] = err.Error()
if a.Identifier != "" {
return fmt.Sprintf("acme: authorization error for %s: %s", a.Identifier, strings.Join(e, "; "))
return fmt.Sprintf("acme: authorization error: %s", strings.Join(e, "; "))
// OrderError is returned from Client's order related methods.
// It indicates the order is unusable and the clients should start over with
// AuthorizeOrder.
// The clients can still fetch the order object from CA using GetOrder
// to inspect its state.
type OrderError struct {
OrderURL string
Status string
func (oe *OrderError) Error() string {
return fmt.Sprintf("acme: order %s status: %s", oe.OrderURL, oe.Status)
// RateLimit reports whether err represents a rate limit error and
// any Retry-After duration returned by the server.
// See the following for more details on rate limiting:
func RateLimit(err error) (time.Duration, bool) {
e, ok := err.(*Error)
if !ok {
return 0, false
// Some CA implementations may return incorrect values.
// Use case-insensitive comparison.
if !strings.HasSuffix(strings.ToLower(e.ProblemType), ":ratelimited") {
return 0, false
if e.Header == nil {
return 0, true
return retryAfter(e.Header.Get("Retry-After")), true
// Account is a user account. It is associated with a private key.
// Non-RFC 8555 fields are empty when interfacing with a compliant CA.
type Account struct {
// URI is the account unique ID, which is also a URL used to retrieve
// account data from the CA.
// When interfacing with RFC 8555-compliant CAs, URI is the "kid" field
// value in JWS signed requests.
URI string
// Contact is a slice of contact info used during registration.
// See for supported
// formats.
Contact []string
// Status indicates current account status as returned by the CA.
// Possible values are StatusValid, StatusDeactivated, and StatusRevoked.
Status string
// OrdersURL is a URL from which a list of orders submitted by this account
// can be fetched.
OrdersURL string
// The terms user has agreed to.
// A value not matching CurrentTerms indicates that the user hasn't agreed
// to the actual Terms of Service of the CA.
// It is non-RFC 8555 compliant. Package users can store the ToS they agree to
// during Client's Register call in the prompt callback function.
AgreedTerms string
// Actual terms of a CA.
// It is non-RFC 8555 compliant. Use Directory's Terms field.
// When a CA updates their terms and requires an account agreement,
// a URL at which instructions to do so is available in Error's Instance field.
CurrentTerms string
// Authz is the authorization URL used to initiate a new authz flow.
// It is non-RFC 8555 compliant. Use Directory's AuthzURL or OrderURL.
Authz string
// Authorizations is a URI from which a list of authorizations
// granted to this account can be fetched via a GET request.
// It is non-RFC 8555 compliant and is obsoleted by OrdersURL.
Authorizations string
// Certificates is a URI from which a list of certificates
// issued for this account can be fetched via a GET request.
// It is non-RFC 8555 compliant and is obsoleted by OrdersURL.
Certificates string
// ExternalAccountBinding represents an arbitrary binding to an account of
// the CA which the ACME server is tied to.
// See for more details.
ExternalAccountBinding *ExternalAccountBinding
// ExternalAccountBinding contains the data needed to form a request with
// an external account binding.
// See for more details.
type ExternalAccountBinding struct {
// KID is the Key ID of the symmetric MAC key that the CA provides to
// identify an external account from ACME.
KID string
// Key is the bytes of the symmetric key that the CA provides to identify
// the account. Key must correspond to the KID.
Key []byte
// Algorithm used to sign the JWS.
Algorithm MACAlgorithm
func (e *ExternalAccountBinding) String() string {
return fmt.Sprintf("&{KID: %q, Key: redacted, Algorithm: %v}", e.KID, e.Algorithm)
// Directory is ACME server discovery data.
// See for more details.
type Directory struct {
// NonceURL indicates an endpoint where to fetch fresh nonce values from.
NonceURL string
// RegURL is an account endpoint URL, allowing for creating new accounts.
// Pre-RFC 8555 CAs also allow modifying existing accounts at this URL.
RegURL string
// OrderURL is used to initiate the certificate issuance flow
// as described in RFC 8555.
OrderURL string
// AuthzURL is used to initiate identifier pre-authorization flow.
// Empty string indicates the flow is unsupported by the CA.
AuthzURL string
// CertURL is a new certificate issuance endpoint URL.
// It is non-RFC 8555 compliant and is obsoleted by OrderURL.
CertURL string
// RevokeURL is used to initiate a certificate revocation flow.
RevokeURL string
// KeyChangeURL allows to perform account key rollover flow.
KeyChangeURL 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
// ExternalAccountRequired indicates that the CA requires for all account-related
// requests to include external account binding information.
ExternalAccountRequired bool
// rfcCompliant reports whether the ACME server implements RFC 8555.
// Note that some servers may have incomplete RFC implementation
// even if the returned value is true.
// If rfcCompliant reports false, the server most likely implements draft-02.
func (d *Directory) rfcCompliant() bool {
return d.OrderURL != ""
// Order represents a client's request for a certificate.
// It tracks the request flow progress through to issuance.
type Order struct {
// URI uniquely identifies an order.
URI string
// Status represents the current status of the order.
// It indicates which action the client should take.
// Possible values are StatusPending, StatusReady, StatusProcessing, StatusValid and StatusInvalid.
// Pending means the CA does not believe that the client has fulfilled the requirements.
// Ready indicates that the client has fulfilled all the requirements and can submit a CSR
// to obtain a certificate. This is done with Client's CreateOrderCert.
// Processing means the certificate is being issued.
// Valid indicates the CA has issued the certificate. It can be downloaded
// from the Order's CertURL. This is done with Client's FetchCert.
// Invalid means the certificate will not be issued. Users should consider this order
// abandoned.
Status string
// Expires is the timestamp after which CA considers this order invalid.
Expires time.Time
// Identifiers contains all identifier objects which the order pertains to.
Identifiers []AuthzID
// NotBefore is the requested value of the notBefore field in the certificate.
NotBefore time.Time
// NotAfter is the requested value of the notAfter field in the certificate.
NotAfter time.Time
// AuthzURLs represents authorizations to complete before a certificate
// for identifiers specified in the order can be issued.
// It also contains unexpired authorizations that the client has completed
// in the past.
// Authorization objects can be fetched using Client's GetAuthorization method.
// The required authorizations are dictated by CA policies.
// There may not be a 1:1 relationship between the identifiers and required authorizations.
// Required authorizations can be identified by their StatusPending status.
// For orders in the StatusValid or StatusInvalid state these are the authorizations
// which were completed.
AuthzURLs []string
// FinalizeURL is the endpoint at which a CSR is submitted to obtain a certificate
// once all the authorizations are satisfied.
FinalizeURL string
// CertURL points to the certificate that has been issued in response to this order.
CertURL string
// The error that occurred while processing the order as received from a CA, if any.
Error *Error
// OrderOption allows customizing Client.AuthorizeOrder call.
type OrderOption interface {
// WithOrderNotBefore sets order's NotBefore field.
func WithOrderNotBefore(t time.Time) OrderOption {
return orderNotBeforeOpt(t)
// WithOrderNotAfter sets order's NotAfter field.
func WithOrderNotAfter(t time.Time) OrderOption {
return orderNotAfterOpt(t)
type orderNotBeforeOpt time.Time
func (orderNotBeforeOpt) privateOrderOpt() {}
type orderNotAfterOpt time.Time
func (orderNotAfterOpt) privateOrderOpt() {}
// Authorization encodes an authorization response.
type Authorization struct {
// URI uniquely identifies a authorization.
URI string
// Status is the current status of an authorization.
// Possible values are StatusPending, StatusValid, StatusInvalid, StatusDeactivated,
// StatusExpired and StatusRevoked.
Status string
// Identifier is what the account is authorized to represent.
Identifier AuthzID
// The timestamp after which the CA considers the authorization invalid.
Expires time.Time
// Wildcard is true for authorizations of a wildcard domain name.
Wildcard bool
// Challenges that the client needs to fulfill in order to prove possession
// of the identifier (for pending authorizations).
// For valid authorizations, the challenge that was validated.
// For invalid authorizations, the challenge that was attempted and failed.
// RFC 8555 compatible CAs require users to fuflfill only one of the challenges.
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.
// This field is unused in RFC 8555.
Combinations [][]int
// AuthzID is an identifier that an account is authorized to represent.
type AuthzID struct {
Type string // The type of identifier, "dns" or "ip".
Value string // The identifier itself, e.g. "".
// DomainIDs creates a slice of AuthzID with "dns" identifier type.
func DomainIDs(names ...string) []AuthzID {
a := make([]AuthzID, len(names))
for i, v := range names {
a[i] = AuthzID{Type: "dns", Value: v}
return a
// IPIDs creates a slice of AuthzID with "ip" identifier type.
// Each element of addr is textual form of an address as defined
// in RFC1123 Section 2.1 for IPv4 and in RFC5952 Section 4 for IPv6.
func IPIDs(addr ...string) []AuthzID {
a := make([]AuthzID, len(addr))
for i, v := range addr {
a[i] = AuthzID{Type: "ip", Value: v}
return a
// wireAuthzID is ACME JSON representation of authorization identifier objects.
type wireAuthzID struct {
Type string `json:"type"`
Value string `json:"value"`
// wireAuthz is ACME JSON representation of Authorization objects.
type wireAuthz struct {
Identifier wireAuthzID
Status string
Expires time.Time
Wildcard bool
Challenges []wireChallenge
Combinations [][]int
Error *wireError
func (z *wireAuthz) authorization(uri string) *Authorization {
a := &Authorization{
URI: uri,
Status: z.Status,
Identifier: AuthzID{Type: z.Identifier.Type, Value: z.Identifier.Value},
Expires: z.Expires,
Wildcard: z.Wildcard,
Challenges: make([]*Challenge, len(z.Challenges)),
Combinations: z.Combinations, // shallow copy
for i, v := range z.Challenges {
a.Challenges[i] = v.challenge()
return a
func (z *wireAuthz) error(uri string) *AuthorizationError {
err := &AuthorizationError{
URI: uri,
Identifier: z.Identifier.Value,
if z.Error != nil {
err.Errors = append(err.Errors, z.Error.error(nil))
for _, raw := range z.Challenges {
if raw.Error != nil {
err.Errors = append(err.Errors, raw.Error.error(nil))
return err
// Challenge encodes a returned CA challenge.
// Its Error field may be non-nil if the challenge is part of an Authorization
// with StatusInvalid.
type Challenge struct {
// Type is the challenge type, e.g. "http-01", "tls-alpn-01", "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.
// In RFC 8555, possible values are StatusPending, StatusProcessing, StatusValid,
// and StatusInvalid.
Status string
// Validated is the time at which the CA validated this challenge.
// Always zero value in pre-RFC 8555.
Validated time.Time
// Error indicates the reason for an authorization failure
// when this challenge was used.
// The type of a non-nil value is *Error.
Error error
// wireChallenge is ACME JSON challenge representation.
type wireChallenge struct {
URL string `json:"url"` // RFC
URI string `json:"uri"` // pre-RFC
Type string
Token string
Status string
Validated time.Time
Error *wireError
func (c *wireChallenge) challenge() *Challenge {
v := &Challenge{
Type: c.Type,
Token: c.Token,
Status: c.Status,
if v.URI == "" {
v.URI = c.URI // c.URL was empty; use legacy
if v.Status == "" {
v.Status = StatusPending
if c.Error != nil {
v.Error = c.Error.error(nil)
return v
// wireError is a subset of fields of the Problem Details object
// as described in
type wireError struct {
Status int
Type string
Detail string
Instance string
func (e *wireError) error(h http.Header) *Error {
return &Error{
StatusCode: e.Status,
ProblemType: e.Type,
Detail: e.Detail,
Instance: e.Instance,
Header: h,
// CertOption is an optional argument type for the TLS ChallengeCert methods for
// customizing a temporary certificate for TLS-based challenges.
type CertOption interface {
// WithKey creates an option holding a private/public key pair.
// The private part signs a certificate, and the public part represents the signee.
func WithKey(key crypto.Signer) CertOption {
return &certOptKey{key}
type certOptKey struct {
key crypto.Signer
func (*certOptKey) privateCertOpt() {}
// WithTemplate creates an option for specifying a certificate template.
// See x509.CreateCertificate for template usage details.
// In TLS ChallengeCert methods, the template is also used as parent,
// resulting in a self-signed certificate.
// The DNSNames field of t is always overwritten for tls-sni challenge certs.
func WithTemplate(t *x509.Certificate) CertOption {
return (*certOptTemplate)(t)
type certOptTemplate x509.Certificate
func (*certOptTemplate) privateCertOpt() {}