According to the GraphQL spec, extensions should be supported in the response map. Reference https://spec.graphql.org/October2021/#sel-EAPHJCAACCoGu9J
The response map may also contain an entry with key extensions. This entry, if set, must have a map as its value. This entry is reserved for implementors to extend the protocol however they see fit, and hence there are no additional restrictions on its contents.
How does one set that map in a graphene resolver method? The documentation doesn't show that.