#15: implement ACME certificate store, Traefik/Coolify cert watcher & secrets vault

services/protocols/internal/infrastructure/acme/issuer.go

@@ -0,0 +1,236 @@
+// Package acme implements mode B of PLAN.md section 8.3: LambdaMail obtains
+// and renews the mail host's certificate itself, instead of reading the one
+// Traefik manages.
+//
+// The reason this mode exists at all is DANE. Traefik cannot be told to reuse
+// a key we generated, and DANE requires exactly that: the TLSA association for
+// the next certificate has to be published, and allowed to propagate, before
+// that certificate is served. Without a pre-generated key there is always a
+// window in which the published association does not match the certificate,
+// and every validating receiver rejects mail during it (PLAN.md section 5.1).
+package acme
+
+import (
+	"context"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"time"
+
+	"github.com/go-acme/lego/v4/certcrypto"
+	"github.com/go-acme/lego/v4/certificate"
+	"github.com/go-acme/lego/v4/lego"
+	"github.com/go-acme/lego/v4/providers/dns/cloudflare"
+	"github.com/go-acme/lego/v4/registration"
+
+	"lambdamail/protocols/internal/application/port"
+)
+
+// LetsEncryptProduction and LetsEncryptStaging are the two directories worth
+// naming. Staging exists because the production rate limits are strict enough
+// that a misconfigured deploy loop can lock a domain out for a week.
+const (
+	LetsEncryptProduction = "https://acme-v02.api.letsencrypt.org/directory"
+	LetsEncryptStaging    = "https://acme-staging-v02.api.letsencrypt.org/directory"
+)
+
+// Issuer obtains certificates over ACME with the DNS-01 challenge.
+//
+// DNS-01 is used rather than HTTP-01 because the mail host does not
+// necessarily serve HTTP, and because it is the only challenge that can issue
+// a wildcard.
+type Issuer struct {
+	store           port.CertificateStore
+	email           string
+	directoryURL    string
+	cloudflareToken string
+}
+
+func NewIssuer(store port.CertificateStore, email, directoryURL, cloudflareToken string) *Issuer {
+	if directoryURL == "" {
+		directoryURL = LetsEncryptProduction
+	}
+	return &Issuer{
+		store:           store,
+		email:           email,
+		directoryURL:    directoryURL,
+		cloudflareToken: cloudflareToken,
+	}
+}
+
+// acmeUser adapts the stored account key to lego's registration.User.
+type acmeUser struct {
+	email        string
+	key          crypto.PrivateKey
+	registration *registration.Resource
+}
+
+func (u *acmeUser) GetEmail() string                        { return u.email }
+func (u *acmeUser) GetRegistration() *registration.Resource { return u.registration }
+func (u *acmeUser) GetPrivateKey() crypto.PrivateKey        { return u.key }
+
+// GeneratePrivateKey produces a key for the next certificate. It is exported
+// because the rollover generates the key well before issuance, so that its
+// TLSA association can be published first.
+func GeneratePrivateKey() ([]byte, error) {
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return nil, fmt.Errorf("generate certificate key: %w", err)
+	}
+	der, err := x509.MarshalPKCS8PrivateKey(key)
+	if err != nil {
+		return nil, fmt.Errorf("marshal certificate key: %w", err)
+	}
+	return pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: der}), nil
+}
+
+// Obtain issues a certificate for the given domains.
+//
+// When privateKeyPEM is supplied the CSR is built against that key, which is
+// what keeps a pre-published TLSA association valid. When it is nil a fresh
+// key is generated, which is correct only for deployments without DANE.
+func (i *Issuer) Obtain(ctx context.Context, domains []string, privateKeyPEM []byte) (*port.StoredCertificate, error) {
+	if len(domains) == 0 {
+		return nil, fmt.Errorf("acme: no domains requested")
+	}
+
+	client, err := i.client(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	request := certificate.ObtainRequest{
+		Domains: domains,
+		Bundle:  true,
+	}
+
+	if privateKeyPEM != nil {
+		key, err := parsePrivateKey(privateKeyPEM)
+		if err != nil {
+			return nil, err
+		}
+		// This is the whole point of mode B: the CA signs a CSR built from a
+		// key we chose, so the association published in advance still matches.
+		request.PrivateKey = key
+	}
+
+	resource, err := client.Certificate.Obtain(request)
+	if err != nil {
+		return nil, fmt.Errorf("acme: obtain certificate for %v: %w", domains, err)
+	}
+
+	notAfter, err := certificateExpiry(resource.Certificate)
+	if err != nil {
+		return nil, err
+	}
+
+	return &port.StoredCertificate{
+		Domain:         domains[0],
+		CertificatePEM: resource.Certificate,
+		PrivateKeyPEM:  resource.PrivateKey,
+		NotAfter:       notAfter,
+	}, nil
+}
+
+// client builds a lego client, reusing the stored account key so that every
+// restart does not register a new account with the CA.
+func (i *Issuer) client(ctx context.Context) (*lego.Client, error) {
+	accountKeyPEM, err := i.store.LoadAccountKey(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("acme: load account key: %w", err)
+	}
+
+	newAccount := accountKeyPEM == nil
+	if newAccount {
+		if accountKeyPEM, err = GeneratePrivateKey(); err != nil {
+			return nil, err
+		}
+	}
+
+	accountKey, err := parsePrivateKey(accountKeyPEM)
+	if err != nil {
+		return nil, err
+	}
+
+	user := &acmeUser{email: i.email, key: accountKey}
+
+	config := lego.NewConfig(user)
+	config.CADirURL = i.directoryURL
+	config.Certificate.KeyType = certcrypto.EC256
+
+	client, err := lego.NewClient(config)
+	if err != nil {
+		return nil, fmt.Errorf("acme: create client: %w", err)
+	}
+
+	provider, err := cloudflare.NewDNSProviderConfig(&cloudflare.Config{
+		AuthToken: i.cloudflareToken,
+		// The challenge record has to be visible before the CA looks, so the
+		// provider polls until it can see it itself.
+		PropagationTimeout: 5 * time.Minute,
+		PollingInterval:    10 * time.Second,
+		TTL:                120,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("acme: create cloudflare dns provider: %w", err)
+	}
+	if err := client.Challenge.SetDNS01Provider(provider); err != nil {
+		return nil, fmt.Errorf("acme: configure dns-01 challenge: %w", err)
+	}
+
+	if newAccount {
+		reg, err := client.Registration.Register(registration.RegisterOptions{TermsOfServiceAgreed: true})
+		if err != nil {
+			return nil, fmt.Errorf("acme: register account: %w", err)
+		}
+		user.registration = reg
+
+		if err := i.store.SaveAccountKey(ctx, accountKeyPEM); err != nil {
+			return nil, fmt.Errorf("acme: save account key: %w", err)
+		}
+	} else {
+		reg, err := client.Registration.ResolveAccountByKey()
+		if err != nil {
+			return nil, fmt.Errorf("acme: resolve existing account: %w", err)
+		}
+		user.registration = reg
+	}
+
+	return client, nil
+}
+
+func parsePrivateKey(pemBytes []byte) (crypto.PrivateKey, error) {
+	block, _ := pem.Decode(pemBytes)
+	if block == nil {
+		return nil, fmt.Errorf("acme: private key is not valid PEM")
+	}
+
+	if key, err := x509.ParsePKCS8PrivateKey(block.Bytes); err == nil {
+		return key, nil
+	}
+	if key, err := x509.ParseECPrivateKey(block.Bytes); err == nil {
+		return key, nil
+	}
+	key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("acme: parse private key: %w", err)
+	}
+	return key, nil
+}
+
+// certificateExpiry reads the leaf's NotAfter, which is what drives renewal.
+func certificateExpiry(chainPEM []byte) (time.Time, error) {
+	block, _ := pem.Decode(chainPEM)
+	if block == nil {
+		return time.Time{}, fmt.Errorf("acme: issued certificate is not valid PEM")
+	}
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("acme: parse issued certificate: %w", err)
+	}
+	return cert.NotAfter, nil
+}