Add helper for generating better permission denied errors

acl/errors.go

@@ -2,6 +2,7 @@ package acl
 
 import (
 	"errors"
+	"fmt"
 	"strings"
 )
 
@@ -70,3 +71,8 @@ func (e PermissionDeniedError) Error() string {
 	}
 	return errPermissionDenied
 }
+
+func PermissionDenied(msg string, args ...interface{}) PermissionDeniedError {
+	cause := fmt.Sprintf(msg, args...)
+	return PermissionDeniedError{Cause: cause}
+}