more customer

internal/customerauth/password.go

@@ -0,0 +1,76 @@
+// Package customerauth adds password-based signup/login to the profile service.
+//
+// It deliberately uses only the standard library: PBKDF2-HMAC-SHA256 for
+// password hashing (crypto/pbkdf2, Go 1.24+) and HMAC-SHA256-signed cookies for
+// sessions (crypto/hmac). No password ever leaves the server in plaintext and
+// the session token is opaque + tamper-evident.
+package customerauth
+
+import (
+	"crypto/pbkdf2"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// pbkdf2Iterations is the work factor for PBKDF2-HMAC-SHA256. 210_000 matches
+// the current OWASP recommendation for PBKDF2-SHA256.
+const pbkdf2Iterations = 210_000
+
+const (
+	saltLen = 16
+	keyLen  = 32
+)
+
+// HashPassword returns an encoded PBKDF2 hash of the form
+//
+//	pbkdf2-sha256$<iterations>$<saltB64>$<hashB64>
+//
+// with a fresh random salt. The encoded string is self-describing so Verify can
+// read the parameters back without external configuration.
+func HashPassword(password string) (string, error) {
+	salt := make([]byte, saltLen)
+	if _, err := rand.Read(salt); err != nil {
+		return "", fmt.Errorf("customerauth: read salt: %w", err)
+	}
+	dk, err := pbkdf2.Key(sha256.New, password, salt, pbkdf2Iterations, keyLen)
+	if err != nil {
+		return "", fmt.Errorf("customerauth: pbkdf2: %w", err)
+	}
+	return fmt.Sprintf("pbkdf2-sha256$%d$%s$%s",
+		pbkdf2Iterations,
+		base64.RawStdEncoding.EncodeToString(salt),
+		base64.RawStdEncoding.EncodeToString(dk),
+	), nil
+}
+
+// VerifyPassword reports whether password matches the encoded hash. It is
+// constant-time in the hash comparison and returns false for any malformed
+// encoding rather than erroring, so callers can treat it as a simple predicate.
+func VerifyPassword(password, encoded string) bool {
+	parts := strings.Split(encoded, "$")
+	if len(parts) != 4 || parts[0] != "pbkdf2-sha256" {
+		return false
+	}
+	iter, err := strconv.Atoi(parts[1])
+	if err != nil || iter <= 0 {
+		return false
+	}
+	salt, err := base64.RawStdEncoding.DecodeString(parts[2])
+	if err != nil {
+		return false
+	}
+	want, err := base64.RawStdEncoding.DecodeString(parts[3])
+	if err != nil {
+		return false
+	}
+	got, err := pbkdf2.Key(sha256.New, password, salt, iter, len(want))
+	if err != nil {
+		return false
+	}
+	return subtle.ConstantTimeCompare(got, want) == 1
+}