pinning + new version of backups

Overlord-Client/cmd/agent/tlsconfig/tlsconfig.go

@@ -0,0 +1,106 @@
+package tlsconfig
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+	"time"
+)
+
+type Options struct {
+	InsecureSkipVerify bool
+	CAPath             string
+	SPKIPins           []string
+	ClientCertPath     string
+	ClientKeyPath      string
+}
+
+func Build(options Options) (*tls.Config, error) {
+	pins, err := decodePins(options.SPKIPins)
+	if err != nil {
+		return nil, err
+	}
+
+	tlsConfig := &tls.Config{
+		MinVersion: tls.VersionTLS12,
+	}
+
+	if strings.TrimSpace(options.CAPath) != "" {
+		caCert, err := os.ReadFile(options.CAPath)
+		if err != nil {
+			return nil, fmt.Errorf("read TLS CA: %w", err)
+		}
+		caCertPool := x509.NewCertPool()
+		if !caCertPool.AppendCertsFromPEM(caCert) {
+			return nil, errors.New("parse TLS CA: no certificates found")
+		}
+		tlsConfig.RootCAs = caCertPool
+	}
+
+	if strings.TrimSpace(options.ClientCertPath) != "" || strings.TrimSpace(options.ClientKeyPath) != "" {
+		if strings.TrimSpace(options.ClientCertPath) == "" || strings.TrimSpace(options.ClientKeyPath) == "" {
+			return nil, errors.New("both TLS client certificate and key are required")
+		}
+		certificate, err := tls.LoadX509KeyPair(options.ClientCertPath, options.ClientKeyPath)
+		if err != nil {
+			return nil, fmt.Errorf("load TLS client certificate: %w", err)
+		}
+		tlsConfig.Certificates = []tls.Certificate{certificate}
+	}
+
+	if len(pins) > 0 {
+		// Verification is performed below against an embedded application pin.
+		// This intentionally supports self-signed certificates without trusting
+		// arbitrary certificates from the network or host trust store.
+		tlsConfig.InsecureSkipVerify = true //nolint:gosec
+		tlsConfig.VerifyConnection = func(state tls.ConnectionState) error {
+			return verifyPinnedConnection(state, pins, time.Now())
+		}
+		return tlsConfig, nil
+	}
+
+	tlsConfig.InsecureSkipVerify = options.InsecureSkipVerify //nolint:gosec
+	return tlsConfig, nil
+}
+
+func decodePins(values []string) ([][]byte, error) {
+	result := make([][]byte, 0, len(values))
+	for _, value := range values {
+		value = strings.TrimSpace(strings.TrimPrefix(value, "sha256/"))
+		if value == "" {
+			continue
+		}
+		decoded, err := base64.StdEncoding.DecodeString(value)
+		if err != nil || len(decoded) != sha256.Size {
+			return nil, fmt.Errorf("invalid TLS SPKI pin %q", value)
+		}
+		result = append(result, decoded)
+	}
+	return result, nil
+}
+
+func verifyPinnedConnection(state tls.ConnectionState, pins [][]byte, now time.Time) error {
+	if len(state.PeerCertificates) == 0 {
+		return errors.New("TLS peer did not provide a certificate")
+	}
+	leaf := state.PeerCertificates[0]
+	if now.Before(leaf.NotBefore) || now.After(leaf.NotAfter) {
+		return fmt.Errorf("TLS peer certificate is not valid at %s", now.UTC().Format(time.RFC3339))
+	}
+	sum := sha256.Sum256(leaf.RawSubjectPublicKeyInfo)
+	for _, pin := range pins {
+		if bytes.Equal(sum[:], pin) {
+			return nil
+		}
+	}
+	return fmt.Errorf(
+		"TLS server identity pin mismatch (received sha256/%s)",
+		base64.StdEncoding.EncodeToString(sum[:]),
+	)
+}