lego/certificate/renewal.go

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package certificate
import (
"crypto/x509"
"encoding/asn1"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"math/rand"
"time"
"github.com/go-acme/lego/v4/acme"
)
// RenewalInfoRequest contains the necessary renewal information.
type RenewalInfoRequest struct {
Cert *x509.Certificate
}
// RenewalInfoResponse is a wrapper around acme.RenewalInfoResponse that provides a method for determining when to renew a certificate.
type RenewalInfoResponse struct {
acme.RenewalInfoResponse
// RetryAfter header indicating the polling interval that the ACME server recommends.
// Conforming clients SHOULD query the renewalInfo URL again after the RetryAfter period has passed,
// as the server may provide a different suggestedWindow.
// https://datatracker.ietf.org/doc/html/draft-ietf-acme-ari-03#section-4.2
RetryAfter time.Duration
}
// ShouldRenewAt determines the optimal renewal time based on the current time (UTC),renewal window suggest by ARI, and the client's willingness to sleep.
// It returns a pointer to a time.Time value indicating when the renewal should be attempted or nil if deferred until the next normal wake time.
// This method implements the RECOMMENDED algorithm described in draft-ietf-acme-ari.
//
// - (4.1-11. Getting Renewal Information) https://datatracker.ietf.org/doc/draft-ietf-acme-ari/
func (r *RenewalInfoResponse) ShouldRenewAt(now time.Time, willingToSleep time.Duration) *time.Time {
// Explicitly convert all times to UTC.
now = now.UTC()
start := r.SuggestedWindow.Start.UTC()
end := r.SuggestedWindow.End.UTC()
// Select a uniform random time within the suggested window.
window := end.Sub(start)
randomDuration := time.Duration(rand.Int63n(int64(window)))
rt := start.Add(randomDuration)
// If the selected time is in the past, attempt renewal immediately.
if rt.Before(now) {
return &now
}
// Otherwise, if the client can schedule itself to attempt renewal at exactly the selected time, do so.
willingToSleepUntil := now.Add(willingToSleep)
if willingToSleepUntil.After(rt) || willingToSleepUntil.Equal(rt) {
return &rt
}
// TODO: Otherwise, if the selected time is before the next time that the client would wake up normally, attempt renewal immediately.
// Otherwise, sleep until the next normal wake time, re-check ARI, and return to Step 1.
return nil
}
// GetRenewalInfo sends a request to the ACME server's renewalInfo endpoint to obtain a suggested renewal window.
// The caller MUST provide the certificate and issuer certificate for the certificate they wish to renew.
// The caller should attempt to renew the certificate at the time indicated by the ShouldRenewAt method of the returned RenewalInfoResponse object.
//
// Note: this endpoint is part of a draft specification, not all ACME servers will implement it.
// This method will return api.ErrNoARI if the server does not advertise a renewal info endpoint.
//
// https://datatracker.ietf.org/doc/draft-ietf-acme-ari
func (c *Certifier) GetRenewalInfo(req RenewalInfoRequest) (*RenewalInfoResponse, error) {
certID, err := MakeARICertID(req.Cert)
if err != nil {
return nil, fmt.Errorf("error making certID: %w", err)
}
resp, err := c.core.Certificates.GetRenewalInfo(certID)
if err != nil {
return nil, err
}
defer resp.Body.Close()
var info RenewalInfoResponse
err = json.NewDecoder(resp.Body).Decode(&info)
if err != nil {
return nil, err
}
if retry := resp.Header.Get("Retry-After"); retry != "" {
info.RetryAfter, err = time.ParseDuration(retry + "s")
if err != nil {
return nil, err
}
}
return &info, nil
}
// MakeARICertID constructs a certificate identifier as described in draft-ietf-acme-ari-03, section 4.1.
func MakeARICertID(leaf *x509.Certificate) (string, error) {
if leaf == nil {
return "", errors.New("leaf certificate is nil")
}
// Marshal the Serial Number into DER.
der, err := asn1.Marshal(leaf.SerialNumber)
if err != nil {
return "", err
}
// Check if the DER encoded bytes are sufficient (at least 3 bytes: tag,
// length, and value).
if len(der) < 3 {
return "", errors.New("invalid DER encoding of serial number")
}
// Extract only the integer bytes from the DER encoded Serial Number
// Skipping the first 2 bytes (tag and length).
serial := base64.RawURLEncoding.EncodeToString(der[2:])
// Convert the Authority Key Identifier to base64url encoding without
// padding.
aki := base64.RawURLEncoding.EncodeToString(leaf.AuthorityKeyId)
// Construct the final identifier by concatenating AKI and Serial Number.
return fmt.Sprintf("%s.%s", aki, serial), nil
}