cart and checkout

internal/customerauth/tokens.go

@@ -0,0 +1,62 @@
+package customerauth
+
+import (
+	"crypto/hmac"
+	"encoding/base64"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Purpose-scoped tokens (email verification, password reset) reuse the session
+// Signer's HMAC secret but bind a purpose + subject, so a token minted for one
+// flow cannot be replayed in another. Format:
+//
+//	base64url(<purpose> NUL <subject> NUL <expUnix>) "." base64url(hmac)
+//
+// subject is the normalized email. Like session tokens these are signed, not
+// encrypted: they carry no secret, only a purpose, an email and an expiry, and
+// the HMAC makes them tamper-evident.
+const (
+	purposeVerifyEmail   = "verify"
+	purposePasswordReset = "reset"
+)
+
+// IssuePurpose returns a signed, purpose-bound token for subject that expires
+// after ttl.
+func (s *Signer) IssuePurpose(purpose, subject string, ttl time.Duration) string {
+	exp := time.Now().Add(ttl).Unix()
+	payload := purpose + "\x00" + subject + "\x00" + strconv.FormatInt(exp, 10)
+	b := base64.RawURLEncoding.EncodeToString([]byte(payload))
+	return b + "." + s.sign(b)
+}
+
+// ParsePurpose verifies a purpose token and returns its subject. It requires the
+// embedded purpose to match want and the token to be unexpired, returning
+// ErrInvalidToken for a bad signature/format/purpose and ErrExpiredToken when
+// the token has expired.
+func (s *Signer) ParsePurpose(want, token string) (string, error) {
+	b, sig, ok := strings.Cut(token, ".")
+	if !ok || b == "" || sig == "" {
+		return "", ErrInvalidToken
+	}
+	if !hmac.Equal([]byte(sig), []byte(s.sign(b))) {
+		return "", ErrInvalidToken
+	}
+	raw, err := base64.RawURLEncoding.DecodeString(b)
+	if err != nil {
+		return "", ErrInvalidToken
+	}
+	parts := strings.Split(string(raw), "\x00")
+	if len(parts) != 3 || parts[0] != want {
+		return "", ErrInvalidToken
+	}
+	exp, err := strconv.ParseInt(parts[2], 10, 64)
+	if err != nil {
+		return "", ErrInvalidToken
+	}
+	if time.Now().Unix() >= exp {
+		return "", ErrExpiredToken
+	}
+	return parts[1], nil
+}