From d9f3b250e0cac90529e9dd2c6806d4f9d46901fb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20G=C3=B3rny?= <mgorny@gentoo.org>
Date: Fri, 3 Jul 2026 13:59:02 +0200
Subject: [PATCH] require padding when decoding base64 on Python 3.15+
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Restore the old behavior of `urlsafe_b64decode()` to require padding
when running on Python 3.15+, in order to fix raising `BadData` in some
cases of malformed input.  This fixes the test failures in "bad payload"
tests that incidentally surface when using zlib-ng as the compression
library.

Fixes #420

Signed-off-by: Michał Górny <mgorny@gentoo.org>
--- a/src/itsdangerous/encoding.py
+++ b/src/itsdangerous/encoding.py
@@ -3,6 +3,7 @@
 import base64
 import string
 import struct
+import sys
 import typing as t
 
 from .exc import BadData
@@ -33,7 +34,10 @@ def base64_decode(string: str | bytes) -> bytes:
     string += b"=" * (-len(string) % 4)
 
     try:
-        return base64.urlsafe_b64decode(string)
+        if sys.version_info >= (3, 15):
+            return base64.urlsafe_b64decode(string, padded=True)
+        else:
+            return base64.urlsafe_b64decode(string)
     except (TypeError, ValueError) as e:
         raise BadData("Invalid base64-encoded data") from e