Django 3.2 introduced two new methods: `sign_object` and
`unsign_object` which can sign/unsign "complex data structures" such as
lists, tuples, dictionaries:
https://docs.djangoproject.com/en/3.2/topics/signing/#django.core.signing.TimestampSigner
Because the methods take an arbitrary serializer (a JSON serializer by
default, but not guaranteed), we cannot be sure of the type of `obj`.
