adapter.http: fix base64 decoding without padding

Many online tools omit the padding when encoding base64url. Thus,
requesters may omit the padding as well, which would cause the decoding
to fail. Thus, we simply always append two padding characters, because
python doesn't complain about too much padding.

basyx/aas/adapter/http.py

@@ -376,7 +376,11 @@ def to_url(self, value: model.Identifier) -> str:
  def to_python(self, value: str) -> model.Identifier:
  value = super().to_python(value)
  try:
- decoded = base64.urlsafe_b64decode(super().to_python(value)).decode(self.encoding)
+ # If the requester omits the base64 padding, an exception will be raised.
+ # However, Python doesn't complain about too much padding,
+ # thus we simply always append two padding characters (==).
+ # See also: https://stackoverflow.com/a/49459036/4780052
+ decoded = base64.urlsafe_b64decode(super().to_python(value) + "==").decode(self.encoding)
  except binascii.Error:
  raise BadRequest(f"Encoded identifier {value} is invalid base64url!")
  except UnicodeDecodeError: