fix(jwe): when decrypt, use the original aad base64 value

#101

Author: lepture

src/joserfc/_rfc7516/json.py

@@ -119,7 +119,9 @@ def __extract_segments(
         "tag": urlsafe_b64decode(base64_segments["tag"]),
     }
     if "aad" in data:
-        aad = urlsafe_b64decode(to_bytes(data["aad"]))
+        base64_segments["aad"] = to_bytes(data["aad"])
+        aad = urlsafe_b64decode(base64_segments["aad"])
+        bytes_segments["aad"] = aad
     else:
         aad = None
     return base64_segments, bytes_segments, aad

src/joserfc/_rfc7516/message.py

@@ -124,9 +124,12 @@ def _perform_decrypt(obj: EncryptionData, registry: JWERegistry) -> None:
     if len(cek) * 8 != enc.cek_size:  # pragma: no cover
         cek = secrets.token_bytes(enc.cek_size // 8)
 
-    aad = json_b64encode(obj.protected)
-    if isinstance(obj, BaseJSONEncryption) and obj.aad:
-        aad = aad + b"." + urlsafe_b64encode(obj.aad)
+    if isinstance(obj, BaseJSONEncryption):
+        aad = json_b64encode(obj.protected)
+        if obj.aad:
+            aad = aad + b"." + obj.base64_segments["aad"]
+    else:
+        aad = obj.base64_segments["aad"]
 
     msg = enc.decrypt(ciphertext, tag, cek, iv, aad)
     if "zip" in obj.protected:

tests/jwe/test_compact.py

@@ -313,3 +313,13 @@ def test_compact_encryption(self):
         self.assertEqual(obj.recipients, [])
         obj.attach_recipient(key, {"kid": "foo"})
         self.assertEqual(obj.protected["kid"], "foo")
+
+    def test_decrypt_from_other_libary(self):
+        token = (
+            "eyJhbGciOiAiZGlyIiwgImVuYyI6ICJBMjU2R0NNIiwgImtpZCI6ICJrLTEifQ."
+            ".UlOr6A5mRw3K1Wxx.8lI1604.2ubm__cUeWUB5Q7E8fpkyw"
+        )
+        key = OctKey.import_key(b"\x01" * 32)
+        registry = JWERegistry(algorithms=["dir", "A256GCM"])
+        obj = decrypt_compact(token, key, registry=registry)
+        self.assertEqual(obj.plaintext, b"hello")