first commit

internal/tlsutil/selfsigned.go

@@ -0,0 +1,114 @@
+// Package tlsutil provides certificate loading: LoadOrGenerate for the
+// file/self-signed paths (this file), and ACMEManager (acme_manager.go) for
+// real Let's Encrypt-style issuance via internal/acme. The self-signed
+// generator here remains the fallback for tls.mode "off" or "file" without
+// a cert on disk yet — genuinely necessary for local dev/testing, not a
+// placeholder for a missing feature.
+package tlsutil
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"fmt"
+	"log/slog"
+	"math/big"
+	"net"
+	"time"
+)
+
+// LoadOrGenerate returns a tls.Config for the given mode:
+//   - "file": load cert/key from disk paths
+//   - anything else ("acme" not yet implemented, "off"): generate a self-signed
+//     cert so STARTTLS/IMAPS/etc. still work during development. Logs a loud
+//     warning since this is never appropriate for production.
+func LoadOrGenerate(mode, hostname, certFile, keyFile string, minVersion uint16) (*tls.Config, error) {
+	var cert tls.Certificate
+	var err error
+
+	switch mode {
+	case "file":
+		cert, err = tls.LoadX509KeyPair(certFile, keyFile)
+		if err != nil {
+			return nil, fmt.Errorf("loading TLS cert/key: %w", err)
+		}
+	case "acme":
+		// Reaching here (rather than the real ACMEManager path in main.go)
+		// means mode=="acme" but no acme_domains were configured — a real
+		// ACME client exists (internal/acme, wired in main.go), it's just
+		// not usable without knowing which domain(s) to request a cert for.
+		slog.Warn("TLS mode is 'acme' but no acme_domains are configured — "+
+			"generating a SELF-SIGNED certificate instead. Set tls.acme_domains "+
+			"in config.yaml to enable real Let's Encrypt issuance.",
+			"hostname", hostname)
+		cert, err = generateSelfSigned(hostname)
+		if err != nil {
+			return nil, fmt.Errorf("generating self-signed cert: %w", err)
+		}
+	default:
+		slog.Warn("TLS mode is 'off' — generating a SELF-SIGNED certificate. "+
+			"This is fine for local testing but MUST NOT be used in production; "+
+			"set tls.mode to 'acme' (with acme_domains configured) or 'file'.",
+			"mode", mode, "hostname", hostname)
+		cert, err = generateSelfSigned(hostname)
+		if err != nil {
+			return nil, fmt.Errorf("generating self-signed cert: %w", err)
+		}
+	}
+
+	return &tls.Config{
+		Certificates: []tls.Certificate{cert},
+		MinVersion:   minVersion,
+		ServerName:   hostname,
+	}, nil
+}
+
+// ParseMinVersion converts the config string ("TLS12"/"TLS13") to the
+// crypto/tls constant.
+func ParseMinVersion(s string) uint16 {
+	if s == "TLS13" {
+		return tls.VersionTLS13
+	}
+	return tls.VersionTLS12
+}
+
+func generateSelfSigned(hostname string) (tls.Certificate, error) {
+	priv, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	template := x509.Certificate{
+		SerialNumber: serial,
+		Subject:      pkix.Name{CommonName: hostname, Organization: []string{"GoMail (self-signed, dev only)"}},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().AddDate(1, 0, 0),
+		KeyUsage:     x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		IsCA:         true,
+		BasicConstraintsValid: true,
+	}
+
+	if ip := net.ParseIP(hostname); ip != nil {
+		template.IPAddresses = []net.IP{ip}
+	} else {
+		template.DNSNames = []string{hostname}
+	}
+
+	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	return tls.Certificate{
+		Certificate: [][]byte{derBytes},
+		PrivateKey:  priv,
+	}, nil
+}