Customization of JSONWebTokenMixin field names

[Koldar]

Hi,

loving this library. I'm using it in combination with federations, where multiple services (one per subgraph) authenticate using this library. However, during the merge of the subgraphs, the Apollo gateway complains about:

Field "Mutation.payload" can only be defined once.
Field "Mutation.refreshExpiresIn" can only be defined once.
Field "Mutation.user" can only be defined once.

It makes sense (at least to me), since the there are 2 mutations ObtainJSONWebToken in 2 different subgraphs that are merged together: when merging the output values have the same name, hence the error.

I don't know if this is the correct approach (I'm still a newbie); however, I feel like it should be possible to customize the output name of the ObtainJSONWebToken mutation. I'd be happy to create a pull request about this fix, however if, possible, it would be awesome if you could tell me if this feature is easy to do of if there are some challenges generated by how the library work right now.

Thanks