streamline int overflow check for token timestamps

token/internal/parse/parse.go

@@ -1,9 +1,11 @@
 package parse
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/ucan-wg/go-ucan/did"
+	"github.com/ucan-wg/go-ucan/pkg/policy/limits"
 )
 
 func OptionalDID(s *string) (did.DID, error) {
@@ -13,10 +15,15 @@ func OptionalDID(s *string) (did.DID, error) {
 	return did.Parse(*s)
 }
 
-func OptionalTimestamp(sec *int64) *time.Time {
+func OptionalTimestamp(sec *int64) (*time.Time, error) {
 	if sec == nil {
-		return nil
+		return nil, nil
 	}
+
+	if *sec > limits.MaxInt53 || *sec < limits.MinInt53 {
+		return nil, fmt.Errorf("timestamp value %d exceeds safe integer bounds", *sec)
+	}
+
 	t := time.Unix(*sec, 0)
-	return &t
+	return &t, nil
 }