feat: support time_zone for user registration context

authsession/internal/service/shared/normalize.go

@@ -91,6 +91,20 @@ func ParseClientPublicKey(value string) (common.ClientPublicKey, error) {
 	return key, nil
 }
 
+// ParseTimeZone trims value and validates it as an IANA time zone name.
+func ParseTimeZone(value string) (string, error) {
+	timeZone := NormalizeString(value)
+	if timeZone == "" {
+		return "", InvalidRequest("time_zone must not be empty")
+	}
+
+	if _, err := time.LoadLocation(timeZone); err != nil {
+		return "", InvalidRequest("time_zone must be a valid IANA time zone name")
+	}
+
+	return timeZone, nil
+}
+
 // ParseRevokeReasonCode trims value and validates it as one machine-readable
 // revoke reason code.
 func ParseRevokeReasonCode(value string) (common.RevokeReasonCode, error) {